// mustLinkExternal is a copy of internal/platform.MustLinkExternal,
// duplicated here to avoid version skew in the MustLinkExternal function
// during bootstrapping.
func mustLinkExternal(goos, goarch string, cgoEnabled bool) bool {
	if cgoEnabled {
		switch goarch {
		case "loong64", "mips", "mipsle", "mips64", "mips64le":
			// Internally linking cgo is incomplete on some architectures.
			// https://golang.org/issue/14449
			return true

	}

	cmd := exec.Command(gorootBinGo, "env", "CGO_ENABLED")
	cmd.Stderr = new(bytes.Buffer)
	slurp, err := cmd.Output()
	if err != nil {
		fatalf("Error running %s: %v\n%s", cmd, err, cmd.Stderr)
	}
	parts := strings.Split(string(slurp), "\n")
	if nlines := len(parts) - 1; nlines < 1 {
		fatalf("Error running %s: output contains <1 lines\n%s", cmd, cmd.Stderr)
	}
	t.cgoEnabled, _ = strconv.ParseBool(parts[0])

	env := os.Getenv("CGO_ENABLED")
	if env == "" {
		env = defaultCGO_ENABLED
	}
	switch env {
	case "1":
		c.CgoEnabled = true
	case "0":
		c.CgoEnabled = false
	default:
		// cgo must be explicitly enabled for cross compilation builds
		if runtime.GOARCH == c.GOARCH && runtime.GOOS == c.GOOS {
			c.CgoEnabled = platform.CgoSupported(c.GOOS, c.GOARCH)
			break
		}

		GOARCH       string
		GOEXPERIMENT string
		GODEBUG      string
		CGO_ENABLED  string
	}
	if err := json.NewDecoder(stdout).Decode(&env); err != nil {
		t.Fatal("Decode:", err)
	}
	if err := cmd.Wait(); err != nil {
		t.Fatal("Wait:", err)
	}
	goos = env.GOOS
	goarch = env.GOARCH
	cgoEnabled, _ = strconv.ParseBool(env.CGO_ENABLED)
	goExperiment = env.GOEXPERIMENT
	goDebug = env.GODEBUG

	// CGO_ENABLED.

	tg.setenv("CGO_ENABLED", "1")
	tg.run("list", "-f", "{{.SysoFiles}}", "syso")
	tg.grepStdout("a.syso", "missing syso file with CGO_ENABLED=1")

	tg.setenv("CGO_ENABLED", "0")
	tg.run("list", "-f", "{{.SysoFiles}}", "syso")
	tg.grepStdout("a.syso", "missing syso file with CGO_ENABLED=0")

	tg.setenv("CGO_ENABLED", "1")