cmd = append(cmd, flags...)
		cmd = append(cmd, "-o", "a.exe", long)
		_, err := runcmd(cmd...)
		return err

	case "builddir", "buildrundir":
		// Build an executable from all the .go and .s files in a subdirectory.
		// Run it and verify its output in the buildrundir case.
		longdir := filepath.Join(t.gorootTestDir, t.goDirName())
		files, err := os.ReadDir(longdir)
		if err != nil {
			t.Fatal(err)
		}