message: Fix compile_commands.json parsing when filename is absolute.
  Some compile_commands.json generators will emit absolute paths for the
  filename, such as cmake.
diff: @@ -272,7 +272,11 @@ std::vector<Project::Entry> LoadCompilationEntriesFromDirectory(
  clang_time.Pause(); // TODO: don't call clang::ToString in this block.
  our_time.Resume();
  - std::string absolute_filename = directory + "/" + relative_filename;
  + std::string absolute_filename;
  + if (!relative_filename.empty() && relative_filename[0] == '/')
  + absolute_filename = relative_filename;
  + else
  + absolute_filename = directory + "/" + relative_filename;
  entry.file = NormalizePathWithTestOptOut(absolute_filename);
  entry.directory = directory;
  