message: Switch from C++1z to C++17; corresponds to r319688 in Clang.
diff: @@ -628,7 +628,7 @@ static const clang::LangOptions &GetLangOptions() {
  g_options.CPlusPlus = true;
  g_options.CPlusPlus11 = true;
  g_options.CPlusPlus14 = true;
  - g_options.CPlusPlus1z = true;
  + g_options.CPlusPlus17 = true;
  });
  return g_options;
  }
  