cmd/go: use temporary file for output of gcc command on Windows

On Windows, some of gcc command (like msys2 native) output NUL as a file.

Fixes #36000

Change-Id: I02c632fa2d710a011d79f24d5beee4bc57ad994e
Reviewed-on: https://go-review.googlesource.com/c/go/+/233977
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/go/internal/work/exec.go

@@ -2434,13 +2434,25 @@ func (b *Builder) gccSupportsFlag(compiler []string, flag string) bool {
 	if b.flagCache == nil {
 		b.flagCache = make(map[[2]string]bool)
 	}
+
+	tmp := os.DevNull
+	if runtime.GOOS == "windows" {
+		f, err := ioutil.TempFile(b.WorkDir, "")
+		if err != nil {
+			return false
+		}
+		f.Close()
+		tmp = f.Name()
+		defer os.Remove(tmp)
+	}
+
 	// We used to write an empty C file, but that gets complicated with
 	// go build -n. We tried using a file that does not exist, but that
 	// fails on systems with GCC version 4.2.1; that is the last GPLv2
 	// version of GCC, so some systems have frozen on it.
 	// Now we pass an empty file on stdin, which should work at least for
 	// GCC and clang.
-	cmdArgs := str.StringList(compiler, flag, "-c", "-x", "c", "-", "-o", os.DevNull)
+	cmdArgs := str.StringList(compiler, flag, "-c", "-x", "c", "-", "-o", tmp)
 	if cfg.BuildN || cfg.BuildX {
 		b.Showcmd(b.WorkDir, "%s || true", joinUnambiguously(cmdArgs))
 		if cfg.BuildN {

src/cmd/go/testdata/script/issue36000.txt

@@ -0,0 +1,6 @@
+# Tests golang.org/issue/36000
+
+[!cgo] skip
+
+# go env with CGO flags should not make NUL file
+go env CGO_CFLAGS