Update libevent 2021 component so it also only warns once when detecting reentrant behavior

This commit was SVN r28721.

opal/mca/event/libevent2021/libevent/event.c

@@ -1550,6 +1550,10 @@ event_loop(int flags)
 	return event_base_loop(current_base, flags);
 }
 
+/********* OMPI CHANGE **********/ 
+static int warn_once = 0; 
+/*********/ 
+
 int
 event_base_loop(struct event_base *base, int flags)
 {
@@ -1562,10 +1566,13 @@ event_base_loop(struct event_base *base, int flags)
 	 * as we invoke user callbacks. */
 	EVBASE_ACQUIRE_LOCK(base, th_base_lock);
 
-	if (base->running_loop) {
+	if (base->running_loop && 0 == warn_once) {
 		event_warnx("%s: reentrant invocation.  Only one event_base_loop"
 		    " can run on each event_base at once.", __func__);
-		EVBASE_RELEASE_LOCK(base, th_base_lock);
+                /********* OMPI CHANGE **********/ 
+                warn_once = 1; 
+                /*********/
+                EVBASE_RELEASE_LOCK(base, th_base_lock);
 		return -1;
 	}