message: Fix an unused variable warning in no-assert builds
diff: @@ -320,6 +320,7 @@ MainLoop::RegisterSignal(int signo, const Callback &callback, Status &error) {
  // Even if using kqueue, the signal handler will still be invoked, so it's
  // important to replace it with our "benign" handler.
  int ret = sigaction(signo, &new_action, &info.old_action);
  + (void)ret;
  assert(ret == 0 && "sigaction failed");
  #if HAVE_SYS_EVENT_H
  