message: Avoid unix specific getpid(), isatty().
  Also proper std::filesystem::path string conversion.
diff: @@ -136,11 +136,9 @@ absl::Status FileExists(const std::string &filename) {
  absl::Status GetContents(absl::string_view filename, std::string *content) {
  std::ifstream fs;
  std::istream *stream = nullptr;
  - const bool use_stdin = filename == "-";
  + const bool use_stdin = filename == "-"; // convention: honor "-" as stdin
  if (use_stdin) {
  - // convention: honor "-" as stdin
  stream = &std::cin;
  - if (isatty(0)) std::cerr << "Enter input (terminate with Ctrl-D):\n";
  } else {
  const std::string filename_str = std::string(filename);
  absl::Status usable_file = FileExists(filename_str);
  @@ -200,7 +198,7 @@ absl::StatusOr<Directory> ListDir(absl::string_view dir) {
  }
  for (const fs::directory_entry entry : fs::directory_iterator(d.path)) {
  - const std::string entry_name = entry.path();
  + const std::string entry_name = entry.path().string();
  if (entry.is_directory()) {
  d.directories.push_back(entry_name);
  } else {
  @@ -216,7 +214,7 @@ absl::StatusOr<Directory> ListDir(absl::string_view dir) {
  namespace testing {
  std::string RandomFileBasename(absl::string_view prefix) {
  - return absl::StrCat(prefix, "-", getpid(), "-", random());
  + return absl::StrCat(prefix, "-", rand());
  }
  ScopedTestFile::ScopedTestFile(absl::string_view base_dir,
  