if err != nil {
		return nil, err
	}
	cmd := exec.Command(path, cmdline[1:]...)
	if cmd.Path != "" {
		cmd.Args[0] = cmd.Path
	}
	cmd.Stdout = &buf
	cmd.Stderr = &buf
	cleanup := passLongArgsInResponseFiles(cmd)
	defer cleanup()
	if dir != "." {
		cmd.Dir = dir
	}
	cmd.Env = cmd.Environ() // Pre-allocate with correct PWD.

	// Add the TOOLEXEC_IMPORTPATH environment variable for -toolexec tools.

	abs := make([]string, len(files))
	for i, f := range files {
		if !filepath.IsAbs(f) {
			f = filepath.Join(dir, f)
		}
		abs[i] = f
	}
	return abs
}

// passLongArgsInResponseFiles modifies cmd such that, for
// certain programs, long arguments are passed in "response files", a
// file on disk with the arguments, with one arg per line. An actual