The signature for a pthread function requires that it

return a pointer to a void. The send_thread() and disk_thread()
funtions; however, do not have a return value because they run for
the duration of the daemon's lifetime. This causes gcc to barf when
running with -O3. Make these functions return a null pointer to quiet it.

PR:	bin/124342
Submitted by:	Garrett Cooper <gcooper@FreeBSD.org> (minus his comments)
MFC after:	1 week

sbin/ggate/ggated/ggated.c

@@ -756,6 +756,9 @@ disk_thread(void *arg)
 		error = pthread_mutex_unlock(&outqueue_mtx);
 		assert(error == 0);
 	}
+
+	/* NOTREACHED */
+	return (NULL);
 }
 
 static void *
@@ -810,6 +813,9 @@ send_thread(void *arg)
 		}
 		free(req);
 	}
+
+	/* NOTREACHED */
+	return (NULL);
 }
 
 static void