message: Show doctest help if requested.
diff: @@ -433,6 +433,8 @@ int main(int argc, char** argv) {
  if (HasOption(options, "-h") || HasOption(options, "--help")) {
  PrintHelp();
  + // Also emit doctest help if --test-unit is passed.
  + if (!HasOption(options, "--test-unit"))
  return 0;
  }
  