fix backport issue

src/lib/ares_event_thread.c

@@ -296,13 +296,13 @@ static void *ares_event_thread(void *arg)
     e->ev_sys->wait(e, timeout_ms);
 
     /* Relock before we loop again */
-    ares_thread_mutex_lock(e->mutex);
+    ares__thread_mutex_lock(e->mutex);
 
     /* Each iteration should do timeout processing */
     if (e->isup) {
-      ares_thread_mutex_unlock(e->mutex);
+      ares__thread_mutex_unlock(e->mutex);
       ares_process_fd(e->channel, ARES_SOCKET_BAD, ARES_SOCKET_BAD);
-      ares_thread_mutex_lock(e->mutex);
+      ares__thread_mutex_lock(e->mutex);
     }
   }