cmd: move GOEXPERIMENT knob from make.bash to cmd/go
This CL changes GOEXPERIMENT to act like other GO[CONFIG] environment
variables. Namely, that it can be set at make.bash time to provide a
default value used by the toolchain, but then can be manually set when
running either cmd/go or the individual tools (compiler, assembler,
linker).
For example, it's now possible to test rsc.io/tmp/fieldtrack by simply
running:
GOEXPERIMENT=fieldtrack go test -gcflags=-l rsc.io/tmp/fieldtrack \
-ldflags=-k=rsc.io/tmp/fieldtrack.tracked
without needing to re-run make.bash. (-gcflags=-l is needed because
the compiler's inlining abilities have improved, so calling a function
with a for loop is no longer sufficient to suppress inlining.)
Fixes #42681.
Change-Id: I2cf8995d5d0d05f6785a2ee1d3b54b2cfb3331ca
Reviewed-on: https://go-review.googlesource.com/c/go/+/300991
Trust: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org> Reviewed-by: Bryan C. Mills <bcmills@google.com>