if err != nil {
		// Should not happen - b.CFlags was given an empty package.
		fmt.Fprintf(os.Stderr, "go: invalid cflags: %v\n", err)
		return nil
	}
	cmd := b.GccCmd(".", "")

	join := func(s []string) string {
		q, err := quoted.Join(s)
		if err != nil {
			return strings.Join(s, " ")
		}
		return q
	}

	ret := []cfg.EnvVar{