Updates http2 to x/net/http2 git rev 97aa3a539 for:

    http2: dynamic table updates must occur first
    https://golang.org/cl/111681

    http2: receiving too much data is a protocol error
    https://golang.org/cl/111679

    http2: correct overflow protection
    https://golang.org/cl/111675

    http2: make Server send GOAWAY if Handler sets "Connection: close" header
    https://golang.org/cl/121415

Fixes #20977

Change-Id: I9b8659b5191409ed007e2d911913763bcbabb7cc
Reviewed-on: https://go-review.googlesource.com/121695Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

If the runtime code panics due to a bad index or slice expression,
then throw instead of panicing. This will skip calls to recover and dump
the entire runtime stack trace. The runtime should never panic due to
an out of bounds index, and this will help with debugging if it does.

For #24991
Updates #25201

Change-Id: I85a9feded8f0de914ee1558425931853223c0514
Reviewed-on: https://go-review.googlesource.com/121515Reviewed-by: Austin Clements <austin@google.com>

OpenBSD 6.4 is going to start requiring that the SP points to memory
that was mapped with MAP_STACK on system call entry, traps, and when
switching to the alternate signal stack [1]. Currently, Go doesn't map
any memory MAP_STACK, so the kernel quickly kills Go processes.

Fix this by remapping the memory that backs stack spans with
MAP_STACK, and re-remapping it without MAP_STACK when it's returned to
the heap.

[1] http://openbsd-archive.7691.n7.nabble.com/stack-register-checking-td338238.html

Fixes #26142.

Change-Id: I656eb84385a22833445d49328bb304f8cdd0e225
Reviewed-on: https://go-review.googlesource.com/121657
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

CL 103055 made it so that invalid parameter expansions, like "$|", did
not make the dollar sign silently disappear.

A few edge cases were not taken into account, such as "${}" and "${",
which were now printing just "$". For consistency and to not break
existing programs, go back to eating up the characters when invalid
syntax is encountered.

For completeness, add a "$" test case too, even though its behavior is
unchanged by this CL.

Fixes #26135.

Change-Id: I5d25db9a8356dc6047a8502e318355113a99b247
Reviewed-on: https://go-review.googlesource.com/121636
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

The existing implementation of bytes.Compare on s390x doesn't work properly for slices longer
than 256 elements. This change fixes that. Added tests for long strings and slices of bytes.

Fixes #26114

Change-Id: If6d8b68ee6dbcf99a24f867a1d3438b1f208954f
Reviewed-on: https://go-review.googlesource.com/121495Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

This reverts commit 1a27f048.

Reason for revert: Broke the ssacheck and -N-l builders, and the -N-l fix looks like it will take some time and take a different route entirely.

Change-Id: Ie0ac5e86ab7d72a303dfbbc48dfdf1e092d4f61a
Reviewed-on: https://go-review.googlesource.com/121715Reviewed-by: David Chase <drchase@google.com>

Be super explicit that HTTP keep-alives != TCP keep-alives.

Fixes #26128

Change-Id: I77d74a6fe077259d996543f901a58aa3e49c1093
Reviewed-on: https://go-review.googlesource.com/121616Reviewed-by: Ian Lance Taylor <iant@golang.org>

I thought I removed this but failed to amend it to my commit before
submitting.

Change-Id: I2d687d91f4de72251548faa700006af0fea503af
Reviewed-on: https://go-review.googlesource.com/121615
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>

If one quickly looks at the strings package godoc, reading the name
TrimLeft, one might think it removes a prefix from the string.

The function's godoc does explain its purpose, but it's apparent that it
is not clear enough, as there have been numerous raised issues about
this confusion: #12771 #14657 #18160 #19371 #20085 #25328 #26119. These
questions are also frequent elsewhere on the internet.

Add a very short paragraph to the godoc, to hopefully point new Go
developers in the right direction faster. Do the same thing for
TrimRight and TrimSuffix.

Change-Id: I4dee5ed8dd9fba565b4755bad12ae1ee6d277959
Reviewed-on: https://go-review.googlesource.com/121637Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Fill in the missing descriptions for the CoverBlock struct fields

Change-Id: I9257881a19b01e5cfe61cf19a91375b6d7cc68ef
GitHub-Last-Rev: f5b9e1d49d1c00f59ce4d3684915e5e93ec0297a
GitHub-Pull-Request: golang/go#24079
Reviewed-on: https://go-review.googlesource.com/96756Reviewed-by: Andrew Bonventre <andybons@golang.org>
Run-TryBot: Andrew Bonventre <andybons@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Given a carefully constructed input, writebarrier would
split a block with the OpAddr in the first half and the
VarDef in the second half which ultimately leads to a
compiler crash because the scheduler is no longer able
to put them in the proper order.

To fix, recognize the implicit dependence of OpAddr on
the VarDef of the same symbol if any exists.

This fix was chosen over making OpAddr take a memory
operand to make the dependence explicit, because this
change is less invasive at this late part of the 1.11
release cycle.

Fixes #26105.

Change-Id: I9b65460673af3af41740ef877d2fca91acd336bc
Reviewed-on: https://go-review.googlesource.com/121436
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

SSA can handle 1-element array, but only when the element type
is SSAable. When building SSA for INDEX of 1-element array, we
did not check the element type is SSAable. And when it's not,
it resulted in an unhandled SSA op.

Fixes #26120.

Change-Id: Id709996b5d9d90212f6c56d3f27eed320a4d8360
Reviewed-on: https://go-review.googlesource.com/121496
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>

The check was running in the loop that read source files in, much before
any of the other checks ran. Vetxonly makes vet exit early, but after
all the source files have been read.

To fix this, simply run the buildtag check along with all the other
checks that get run on specific syntax tree nodes.

Add a cmd/go test with go test -a, to ensure that the issue as reported
is fixed.

Fixes #26102.

Change-Id: If6e3b9418ffa8166c0f982668b0d10872283776a
Reviewed-on: https://go-review.googlesource.com/121395
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

Before CL 4281055 in 2011, the reflect package was quite different.
rtype, then called commonType, was embedded in exported structs with
names like StructType. In order to avoid accidental conversions
between pointers to these public structs, which sometimes had
identical fields, the embedded commonType fields were tagged.

In CL 4281055 the formerly public structs were unexported, and all
access was done through the Type interface. At that point the field
tags in the reflect structs were no longer useful.

In Go 1.8 the language was changed to ignore struct field tags when
converting between types. This made the field tags in the reflect
structs doubly useless.

This CL simply removes them.

Fixes #20914

Change-Id: I9af4d6d0709276a91a6b6ee5323cad9dcd0cd0a0
Reviewed-on: https://go-review.googlesource.com/121475
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Fixes #24763.

Change-Id: Ibe534271d75b6961d00ebfd7d42c43a3ac650d79
Reviewed-on: https://go-review.googlesource.com/121335Reviewed-by: Matthew Dempsky <mdempsky@google.com>

The Server distinguishes "new" vs "idle" connections. A TCP connection
from which no bytes have yet been written is "new". A connection that
has previously served a request and is in "keep-alive" state while
waiting for a second or further request is "idle".

The graceful Server.Shutdown historically only shut down "idle"
connections, with the assumption that a "new" connection was about to
read its request and would then shut down on its own afterwards.

But apparently some clients spin up connections and don't end up using
them, so we have something that's "new" to us, but browsers or other
clients are treating as "idle" to them.

This CL tweaks our heuristic to treat a StateNew connection as
StateIdle if it's been stuck in StateNew for over 5 seconds.

Fixes #22682

Change-Id: I01ba59a6ab67755ca5ab567041b1f54aa7b7da6f
Reviewed-on: https://go-review.googlesource.com/121419
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Move badf helper into top-level function so that prints from buildtag.go
are once again themselves printf-format-checked by vet.
Also, fix implementation, which was missing a ... in the Sprintf call and
produced messages like:

/Users/rsc/x_test.go:1: +build comment must appear before package clause and be followed by a blank line%!(EXTRA []interface {}=[])

These were introduced in CL 111415.

Change-Id: I000af3a4e01dc99fc79c9146aa68a71dace1460f
Reviewed-on: https://go-review.googlesource.com/121300
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rob Pike <r@golang.org>

Fix a comment that misrepresented the Assign operator (=).

Rename: colon-equals -> equals.

Change-Id: I405b8acfb0bcd1b176a91a95f9bfb61a4e85815f
GitHub-Last-Rev: aec0bf594c63d7b015f88f97f9953ade976817a4
GitHub-Pull-Request: golang/go#26112
Reviewed-on: https://go-review.googlesource.com/121416Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Code generation for OpAMD64CMOV[WLQ]EQF uses AX as a scratch register,
but only CMOVQEQF, correctly lets compiler know. Mark other 2 as
clobbering AX.

Fixes #26097

Change-Id: I2a65bd67bf18a540898b4a0ae6c8766e0b767b19
Reviewed-on: https://go-review.googlesource.com/121336
Run-TryBot: Ilya Tocar <ilya.tocar@intel.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Heschi Kreinick <heschi@google.com>
Reviewed-by: Giovanni Bajo <rasky@develer.com>

This makes Callback more in line with TypedArray. The name "Release" is
better than "Close" because the function does not implement io.Closer.

Change-Id: I23829a14b1c969ceb04608afd9505fd5b4b0df2e
Reviewed-on: https://go-review.googlesource.com/121216
Run-TryBot: Richard Musiol <neelance@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

The intention was for this file to be constrained to both js and wasm,
but the build constraint was missing, causing it to be constrained only
to js because of the _js suffix in the filename.

Add a js,wasm build constraint. The js part is redundant, but specified
anyway to make it more visible and consistent with other similar files.

This issue was spotted while working on GopherJS, because it was causing
a conflict there (both nonblocking.go and nonblocking_js.go files were
being matched).

Change-Id: Ifc6843269e1108fe61b1723be25a12254e806fd4
Reviewed-on: https://go-review.googlesource.com/121275Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

Now that pkix.Name offers String() we should use that as some CN's are blank.

Updates #24084

Change-Id: I268196f04b98c2bd4d5d0cf1fecd2c9bafeec0f1
Reviewed-on: https://go-review.googlesource.com/121357Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

This reverts commit 0246915f.

Reason for revert: Broke darwin/arm64 builds.

Change-Id: Iead935d345c4776c0f823f4c152e02bdda308401
Reviewed-on: https://go-review.googlesource.com/121375Reviewed-by: Andrew Bonventre <andybons@golang.org>

Currently, the following example cannot run in playground:

    func a() {
        fmt.Println("A")
    }

    func ExampleA() {
        a()
    }

This CL solves it.

Fixes #23095

Change-Id: I5a492ff886a743f20cb4ae646e8453bde9c5f0da
Reviewed-on: https://go-review.googlesource.com/83615
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

This adds support for RSASSA-PSS signatures in handshake messages as
required by TLS 1.3. Even if TLS 1.2 is negotiated, it must support PSS
when advertised in the Client Hello (this will be done later as the
testdata will change).

Updates #9671

Change-Id: I8006b92e017453ae408c153233ce5ccef99b5c3f
Reviewed-on: https://go-review.googlesource.com/79736Reviewed-by: Filippo Valsorda <filippo@golang.org>

On some systems removing files can cause a directory to be re-shuffled,
so simply continuing to read files can cause us to miss some.
Close and re-open the directory when looping, to avoid that.

Read more files each time through the loop, to reduce the chance of
having to re-open.

Fixes #20841

Change-Id: I98a14774ca63786ad05ba5000cbdb01ad2884332
Reviewed-on: https://go-review.googlesource.com/121255
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

The current implementation does not generate wrappers for methods of
embedded non-interface types. We can only skip the wrapper if
kindDirectIface of the generated struct type matches kindDirectIface
of the embedded type. Panic if that is not the case.

It would be better to actually generate wrappers, but that can be done
later.

Updates #15924
Fixes #24782

Change-Id: I01f5c76d9a07f44e1b04861bfe9f9916a04e65ca
Reviewed-on: https://go-review.googlesource.com/121316Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Allow a zone to be included with the ip address that is parsed when
using DefaultResolver's LookupHost or LookupIPAddr

Fixes #20790
Fixes #20767

Change-Id: I4e0baf9ade6a095af10a1b85ca6216788ba680ae
Reviewed-on: https://go-review.googlesource.com/79935
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

The new function js.TypedArrayOf returns a JavaScript typed array for
a given slice.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Typed_arrays

This change also changes js.ValueOf to not accept a []byte any more.

Fixes #25532.

Change-Id: I8c7bc98ca4e21c3514d19eee7a1f92388d74ab2a
Reviewed-on: https://go-review.googlesource.com/121215
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

The current resolver uses a global lookupGroup which merges LookupIPAddr
calls together for lookups for the same hostname if used concurrently.
As a result only one of the resolvers is actually used to perform the
DNS lookup but the result is shared by all the resolvers.

This commit limits the scope of the lookupGroup to the resolver itself
allowing each resolver to make its own requests without sharing the
result with other resolvers.

Fixes #22908

Change-Id: Ibba896eebb05e59f18ce4132564ea1f2b4b6c6d9
Reviewed-on: https://go-review.googlesource.com/80775
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

This patch ports the existing optimized P256 implementation to arm64.

name            old time/op    new time/op    delta
pkg:crypto/ecdsa goos:linux goarch:arm64
SignP256           539µs ±13%      43µs ± 2%  -91.95%  (p=0.000 n=20+20)
SignP384          13.2ms ± 1%    13.2ms ± 1%     ~     (p=0.739 n=10+10)
VerifyP256        1.57ms ± 0%    0.12ms ± 0%  -92.40%  (p=0.000 n=18+20)
KeyGeneration      391µs ± 0%      25µs ± 0%  -93.62%  (p=0.000 n=9+9)
pkg:crypto/elliptic goos:linux goarch:arm64
BaseMult          1.66ms ± 0%    1.65ms ± 1%     ~     (p=0.079 n=9+10)
BaseMultP256       389µs ± 0%      22µs ± 1%  -94.28%  (p=0.000 n=19+20)
ScalarMultP256    1.03ms ± 0%    0.09ms ± 0%  -91.25%  (p=0.000 n=19+20)

name            old alloc/op   new alloc/op   delta
pkg:crypto/ecdsa goos:linux goarch:arm64
SignP256          5.47kB ± 0%    3.20kB ± 0%  -41.50%  (p=0.000 n=20+20)
SignP384          2.32MB ± 0%    2.32MB ± 0%     ~     (p=0.739 n=10+10)
VerifyP256        7.65kB ± 4%    0.98kB ± 0%  -87.24%  (p=0.000 n=20+20)
KeyGeneration     1.41kB ± 0%    0.69kB ± 0%  -51.05%  (p=0.000 n=9+10)
pkg:crypto/elliptic goos:linux goarch:arm64
BaseMult            224B ± 0%      224B ± 0%     ~     (all equal)
BaseMultP256      1.12kB ± 0%    0.29kB ± 0%  -74.29%  (p=0.000 n=20+20)
ScalarMultP256    1.59kB ± 7%    0.26kB ± 0%  -83.91%  (p=0.000 n=20+20)

name            old allocs/op  new allocs/op  delta
pkg:crypto/ecdsa goos:linux goarch:arm64
SignP256            67.0 ± 0%      35.0 ± 0%  -47.76%  (p=0.000 n=20+20)
SignP384           17.5k ± 0%     17.5k ± 0%     ~     (p=0.725 n=10+10)
VerifyP256          97.2 ± 3%      17.0 ± 0%  -82.52%  (p=0.000 n=20+20)
KeyGeneration       21.0 ± 0%      13.0 ± 0%  -38.10%  (p=0.000 n=10+10)
pkg:crypto/elliptic goos:linux goarch:arm64
BaseMult            5.00 ± 0%      5.00 ± 0%     ~     (all equal)
BaseMultP256        16.0 ± 0%       6.0 ± 0%  -62.50%  (p=0.000 n=20+20)
ScalarMultP256      19.9 ± 6%       5.0 ± 0%  -74.87%  (p=0.000 n=20+20)

Fixes #22806

Change-Id: I0f187074f8c3069bf8692d59e2cf95bdc6061fe7
Reviewed-on: https://go-review.googlesource.com/99755
Run-TryBot: Vlad Krasnov <vlad@cloudflare.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brendan McMillion <brendan@cloudflare.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Updates #19761

Change-Id: Iac3bd4c40002f8e348452b50bff54dee3210d447
Reviewed-on: https://go-review.googlesource.com/121236Reviewed-by: Ian Lance Taylor <iant@golang.org>

RFC 2045 doesn't permit non-ASCII bytes, but some systems send them
anyhow. With this change, we accept them. This does make it harder to
validate quotedprintable data, but on balance this seems like the best
approach given the existence of systems that generate invalid data.

Fixes #22597

Change-Id: I9f80f90a60b76ada2b5dea658b8dc8aace56cdbd
Reviewed-on: https://go-review.googlesource.com/121095Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

At least on Darwin, if getaddrinfo can't open a file descriptor it
returns EAI_NONAME ("no such host") rather than a meaningful error.
Limit the number of concurrent getaddrinfo calls to the number of file
descriptors we can open, to make that meaningless error less likely.

We don't apply the same limit to Go lookups, because for that we will
return a meaningful "too many open files" error.

Fixes #25694

Change-Id: I601857190aeb64f11e22b4a834c1c6a722a0788d
Reviewed-on: https://go-review.googlesource.com/121176Reviewed-by: Bryan C. Mills <bcmills@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Some headers, which are set or modified by the http library,
are not written to the standard http.Request.Header and are
not included as part of http.Response.Request.Header.

Exposing all headers alleviates this problem.

This is not a complete solution to 19761 since it does not have http/2 support.

Updates #19761

Change-Id: Ie8d4f702f4f671666b120b332378644f094e288b
Reviewed-on: https://go-review.googlesource.com/67430
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

On Wasm, the offset was not folded into LoweredAddr, so it was
not rematerializeable. This led to the address-taken operation
in some cases generated too early, before the local variable
becoming live. The liveness code thinks the variable live when
the address is taken, then backs it up to live at function
entry, then complains about it, because nothing other than
arguments should be live on entry.

This CL folds the offset into the address operation, so it is
rematerializeable and so generated right before use, after the
variable actually becomes live.

It might be possible to relax the liveness code not to think a
variable live when its address being taken, but until the address
actually being used. But it would be quite complicated. As we're
late in Go 1.11 freeze, it would be better not to do it. Also,
I think the address operation is rematerializeable now on all
architectures, so this is probably less necessary.

This may also be a slight optimization, as the address+offset is
now rematerializeable, which can be generated on the Wasm stack,
without using any "registers" which are emulated by local
variables on Wasm. I don't know how to do benchmarks on Wasm. At
least, cmd/go binary size shrinks 9K.

Fixes #25966.

Change-Id: I01e5869515d6a3942fccdcb857f924a866876e57
Reviewed-on: https://go-review.googlesource.com/120599
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Richard Musiol <neelance@gmail.com>

This is the same retry loop we use in _cgo_try_pthread_create in runtime/cgo.

Fixes #25078

Change-Id: I7ef4d4fc7fb89cbfb674c4f93cbdd7a033dd8983
Reviewed-on: https://go-review.googlesource.com/121096
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Fixes #21219

Change-Id: I1a2ec1afe06586ed33a3a855b77536490cac3a38
Reviewed-on: https://go-review.googlesource.com/121115
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Fixes #26042

Change-Id: Ica16f14a65c03659a19926852cca5e554c99baf1
Reviewed-on: https://go-review.googlesource.com/120935Reviewed-by: Ian Lance Taylor <iant@golang.org>

Revert the code changes of CL 96975 and CL 70931, but keep the tests,
appropriately modified for the code changes. This restores the 1.9
handling of form-data entries with missing or empty file names.

Changing the handling of this simply confused existing programs for no
useful benefit. Go back to the old behavior.

Updates #19183
Fixes #24041

Change-Id: I4ebc32433911e6360b9fd79d8f63a6d884822e0e
Reviewed-on: https://go-review.googlesource.com/121055
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>