cmd/go, cmd/link: set LC_ALL=C when checking if host compiler supports -no-pie

Fixes #15900

Change-Id: Ieada5f4e3b3b2ae358414e013f3090b4b820569b
Reviewed-on: https://go-review.googlesource.com/23536
Run-TryBot: Michael Hudson-Doyle <michael.hudson@canonical.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/go/build.go

@@ -3088,7 +3088,7 @@ func (b *builder) gccSupportsFlag(flag string) bool {
 	}
 	cmd := exec.Command(cmdArgs[0], cmdArgs[1:]...)
 	cmd.Dir = b.work
-	cmd.Env = envForDir(cmd.Dir, os.Environ())
+	cmd.Env = mergeEnvLists([]string{"LC_ALL=C"}, envForDir(cmd.Dir, os.Environ()))
 	out, err := cmd.CombinedOutput()
 	supported := err == nil && !bytes.Contains(out, []byte("unrecognized"))
 	b.flagCache[flag] = supported

src/cmd/link/internal/ld/lib.go

@@ -1235,6 +1235,7 @@ func hostlink() {
 		}
 		cmd := exec.Command(argv[0], "-c", "-no-pie", "trivial.c")
 		cmd.Dir = tmpdir
+		cmd.Env = append([]string{"LC_ALL=C"}, os.Environ()...)
 		out, err := cmd.CombinedOutput()
 		supported := err == nil && !bytes.Contains(out, []byte("unrecognized"))
 		if supported {