14937:f2755950769b tip

$ go install -race cmd/go
$ go test -race -run=none -short -bench=none std

may be required to run several times with bumped GOMAXPROCS.

WARNING: DATA RACE
Write by goroutine 20:
  main.(*builder).cgo()
      src/cmd/go/build.go:1639 +0x317b
  main.(*builder).build()
      src/cmd/go/build.go:688 +0xbdd
  main.func·004()
      src/cmd/go/build.go:570 +0x4bd
  main.func·005()
      src/cmd/go/build.go:619 +0x122

Previous write by goroutine 18:
  main.(*builder).cgo()
      src/cmd/go/build.go:1639 +0x317b
  main.(*builder).build()
      src/cmd/go/build.go:688 +0xbdd
  main.func·004()
      src/cmd/go/build.go:570 +0x4bd
  main.func·005()
      src/cmd/go/build.go:619 +0x122

Goroutine 20 (running) created at:
  main.(*builder).do()
      src/cmd/go/build.go:621 +0x679
  main.runTest()
      src/cmd/go/test.go:385 +0x27ff
  main.main()
      src/cmd/go/main.go:148 +0x786
  runtime.main()
      src/pkg/runtime/proc.c:248 +0x91

Goroutine 18 (running) created at:
  main.(*builder).do()
      src/cmd/go/build.go:621 +0x679
  main.runTest()
      src/cmd/go/test.go:385 +0x27ff
  main.main()
      src/cmd/go/main.go:148 +0x786
  runtime.main()
      src/pkg/runtime/proc.c:248 +0x91