Drops cmd/binary size from 14.41 MiB to 11.42 MiB.

Before:

   text    data     bss     dec     hex filename
8121210 3521696  737960 12380866         bceac2 ../pkg/tool/linux_amd64/compile

bradfitz@dev-bradfitz-debian2:~/go/src$ ls -l ../pkg/tool/linux_amd64/compile
-rwxr-xr-x 1 bradfitz bradfitz 15111272 Mar  8 23:32 ../pkg/tool/linux_amd64/compile

  a2afc0      51312 R html.statictmp_0085
  6753f0      56592 T cmd/internal/obj/x86.doasm
  625480      58080 T cmd/compile/internal/gc.typecheck1
  f34c40      65688 D runtime.trace
  be0a20     133552 D cmd/compile/internal/ppc64.varianttable
  c013e0     265856 D cmd/compile/internal/arm.progtable
  c42260     417280 D cmd/compile/internal/amd64.progtable
  ca8060     417280 D cmd/compile/internal/x86.progtable
  f44ce0     500640 D cmd/internal/obj/arm64.oprange
  d0de60     534208 D cmd/compile/internal/ppc64.progtable
  d90520     667520 D cmd/compile/internal/arm64.progtable
  e334a0     790368 D cmd/compile/internal/mips64.progtable
  a3e8c0    1579362 r runtime.pclntab

After:

   text    data     bss     dec     hex filename
8128226  375954  246432 8750612  858614 ../pkg/tool/linux_amd64/compile

-rwxr-xr-x 1 bradfitz bradfitz 11971432 Mar  8 23:35 ../pkg/tool/linux_amd64/compile

  6436d0      43936 T cmd/compile/internal/gc.walkexpr
  c13ca0      45056 D cmd/compile/internal/ssa.opcodeTable
  5d8ea0      50256 T cmd/compile/internal/gc.(*state).expr
  818c50      50448 T cmd/compile/internal/ssa.rewriteValueAMD64_OpMove
  a2d0e0      51312 R html.statictmp_0085
  6753d0      56592 T cmd/internal/obj/x86.doasm
  625460      58080 T cmd/compile/internal/gc.typecheck1
  c38fe0      65688 D runtime.trace
  a409e0    1578810 r runtime.pclntab

Fixes #14703

Change-Id: I2177596d5c7fd67db0a3c423cd90801cf52adb12
Reviewed-on: https://go-review.googlesource.com/20450Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>