}
	}

	b.id.Lock()
	b.toolIDCache[key] = id
	b.toolIDCache[key+".exe"] = exe
	b.id.Unlock()

	return id, exe, nil
}

// Check if assembler used by gccgo is GNU as.
func assemblerIsGas() bool {
	cmd := exec.Command(BuildToolchain.compiler(), "-print-prog-name=as")
	assembler, err := cmd.Output()
	if err == nil {
		cmd := exec.Command(strings.TrimSpace(string(assembler)), "--version")