message: Fix pragma warnings. Displayed at least by MSVC.
diff: @@ -141,7 +141,7 @@ static CONSTDATA char folder_delimiter = '/';
  #endif
  -#if __GNUC__ < 5
  +#if defined(__GNUC__) && __GNUC__ < 5
  // GCC 4.9 Bug 61489 Wrong warning with -Wmissing-field-initializers
  # pragma GCC diagnostic push
  # pragma GCC diagnostic ignored "-Wmissing-field-initializers"
  @@ -3208,6 +3208,6 @@ locate_native_zone(const std::string& native_tz_name)
  } // namespace date
  -#if __GNUC__ < 5
  +#if defined(__GNUC__) && __GNUC__ < 5
  # pragma GCC diagnostic pop
  #endif
  