message: Make ABSL_DIE_IF_NULL() more useful.
  ... acutally use the __FILE__ and __LINE__ when printing
  the crash.
  Issues:
diff: @@ -36,7 +36,7 @@ namespace verible {
  template <typename T>
  ABSL_MUST_USE_RESULT T DieIfNull(const char* file, int line,
  const char* exprtext, T&& t) {
  - CHECK(t != nullptr) << exprtext;
  + CHECK((t != nullptr)) << file << ":" << line << ": " << exprtext;
  return std::forward<T>(t);
  }
  } // namespace verible
  