fixup! Force all domain threads to exit at caml_do_exit time.

runtime/domain.c

@@ -1631,6 +1631,7 @@ static void stw_terminate_domain(caml_domain_state *domain, void *data,
   if (!pthread_equal(pthread_self(), *(pthread_t *)data)) {
     /* Ask the matching backup thread, if started, to terminate. */
     atomic_store_release(&domain_self->backup_thread_msg, BT_TERMINATE);
+    caml_plat_signal(&domain_self->domain_cond);
     pthread_exit(0);
   }
 }