Prior to stack tracing, inlining could cause
dead pointers to be kept alive in some loops.
See #18336 and CL 31674.

The adjustment removed by this change preserved the inlining status quo
in the face of Node structure changes, to avoid creating new problems.
Now that stack tracing provides precision, these hacks can be removed.

Of course, our inlining code model is already hacky (#17566),
but at least now there will be fewer epicyclical hacks.

Newly inline-able functions in std cmd as a result of this change:

hash/adler32/adler32.go:65:6: can inline (*digest).UnmarshalBinary
hash/fnv/fnv.go:281:6: can inline (*sum32).UnmarshalBinary
hash/fnv/fnv.go:292:6: can inline (*sum32a).UnmarshalBinary
reflect/value.go:1298:6: can inline Value.OverflowComplex
compress/bzip2/bit_reader.go:25:6: can inline newBitReader
encoding/xml/xml.go:365:6: can inline (*Decoder).switchToReader
vendor/golang_org/x/crypto/cryptobyte/builder.go:77:6: can inline (*Builder).AddUint16
crypto/x509/x509.go:1851:58: can inline buildExtensions.func2.1.1
crypto/x509/x509.go:1871:58: can inline buildExtensions.func2.3.1
crypto/x509/x509.go:1883:58: can inline buildExtensions.func2.4.1
cmd/vet/internal/cfg/builder.go:463:6: can inline (*builder).labeledBlock
crypto/tls/handshake_messages.go:1450:6: can inline (*newSessionTicketMsg).marshal
crypto/tls/handshake_server.go:769:6: can inline (*serverHandshakeState).clientHelloInfo
crypto/tls/handshake_messages.go:1171:6: can inline (*nextProtoMsg).unmarshal
cmd/link/internal/amd64/obj.go:40:6: can inline Init
cmd/link/internal/ppc64/obj.go:40:6: can inline Init
net/http/httputil/persist.go:54:6: can inline NewServerConn
net/http/fcgi/child.go:83:6: can inline newResponse
cmd/compile/internal/ssa/poset.go:245:6: can inline (*poset).newnode

Change-Id: I19e8e383a6273849673d35189a9358870665f82f
Reviewed-on: https://go-review.googlesource.com/c/141117
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ilya Tocar <ilya.tocar@intel.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>