cmd/go: data race on (*load.PackageInternal).Gcflags field #31230
Description
The race was observed at head with go test -race cmd/go, but doesn't always reproduce.
WARNING: DATA RACE
Read at 0x00c00037e8b0 by goroutine 17:
cmd/go/internal/work.gcToolchain.gc()
/usr/local/google/home/bcmills/go/src/cmd/go/internal/work/gc.go:105 +0xc83
cmd/go/internal/work.(*gcToolchain).gc()
<autogenerated>:1 +0x107
cmd/go/internal/work.(*Builder).build()
/usr/local/google/home/bcmills/go/src/cmd/go/internal/work/exec.go:642 +0x1fd4
cmd/go/internal/work.(*Builder).Do.func1()
/usr/local/google/home/bcmills/go/src/cmd/go/internal/work/exec.go:107 +0x465
cmd/go/internal/work.(*Builder).Do.func2()
/usr/local/google/home/bcmills/go/src/cmd/go/internal/work/exec.go:164 +0x97
Previous write at 0x00c00037e8b0 by goroutine 16:
cmd/go/internal/load.setToolFlags()
/usr/local/google/home/bcmills/go/src/cmd/go/internal/load/pkg.go:1800 +0x184
cmd/go/internal/load.LoadImportWithFlags()
/usr/local/google/home/bcmills/go/src/cmd/go/internal/load/pkg.go:1726 +0xe9
cmd/go/internal/work.gcToolchain.symabis()
/usr/local/google/home/bcmills/go/src/cmd/go/internal/work/gc.go:307 +0x2ea
cmd/go/internal/work.(*gcToolchain).symabis()
<autogenerated>:1 +0x8c
cmd/go/internal/work.(*Builder).build()
/usr/local/google/home/bcmills/go/src/cmd/go/internal/work/exec.go:606 +0x183f
cmd/go/internal/work.(*Builder).Do.func1()
/usr/local/google/home/bcmills/go/src/cmd/go/internal/work/exec.go:107 +0x465
cmd/go/internal/work.(*Builder).Do.func2()
/usr/local/google/home/bcmills/go/src/cmd/go/internal/work/exec.go:164 +0x97
Goroutine 17 (running) created at:
cmd/go/internal/work.(*Builder).Do()
/usr/local/google/home/bcmills/go/src/cmd/go/internal/work/exec.go:151 +0x66e
cmd/go/internal/test.runTest()
/usr/local/google/home/bcmills/go/src/cmd/go/internal/test/test.go:752 +0x15cf
main.main()
/usr/local/google/home/bcmills/go/src/cmd/go/main.go:213 +0xa09
Goroutine 16 (running) created at:
cmd/go/internal/work.(*Builder).Do()
/usr/local/google/home/bcmills/go/src/cmd/go/internal/work/exec.go:151 +0x66e
cmd/go/internal/test.runTest()
/usr/local/google/home/bcmills/go/src/cmd/go/internal/test/test.go:752 +0x15cf
main.main()
/usr/local/google/home/bcmills/go/src/cmd/go/main.go:213 +0xa09