message: make fs.rs at least build under Windows
diff: @@ -142,7 +142,10 @@ fn test_symlink() {
  let symlink_path = prepare("miri_test_fs_symlink.txt");
  // Creating a symbolic link should succeed.
  + #[cfg(unix)]
  std::os::unix::fs::symlink(&path, &symlink_path).unwrap();
  + #[cfg(windows)]
  + std::os::windows::fs::symlink_file(&path, &symlink_path).unwrap();
  // Test that the symbolic link has the same contents as the file.
  let mut symlink_file = File::open(&symlink_path).unwrap();
  let mut contents = Vec::new();
  