message: [SwiftASTContext] Check if the library path is empty before adding.
diff: @@ -3479,6 +3479,7 @@ GetLibrarySearchPaths(const swift::SearchPathOptions &search_path_opts) {
  // one sitting next to the stdlib we just built, and then fall back to the
  // one in the OS if that's not available.
  std::vector<std::string> paths;
  + if (!search_path_opts.RuntimeLibraryPath.empty())
  paths.push_back(search_path_opts.RuntimeLibraryPath);
  for (std::string path : search_path_opts.LibrarySearchPaths)
  paths.push_back(path);
  