message: Add missing operator== for exit_msg
diff: @@ -43,6 +43,11 @@ struct exit_msg {
  error reason;
  };
  +/// @relates exit_msg
  +inline bool operator==(const exit_msg& x, const exit_msg& y) noexcept {
  + return x.source == y.source && x.reason == y.reason;
  +}
  +
  /// @relates exit_msg
  template <class Inspector>
  typename Inspector::result_type inspect(Inspector& f, exit_msg& x) {
  