replace pthread_yield with POSIX sched_yield

See: http://linux.die.net/man/3/pthread_yield

src/api/api_idnode.c

@@ -651,7 +651,7 @@ api_idnode_handler
       }
       pthread_mutex_unlock(&global_lock);
       if (destroyed)
-        pthread_yield(); /* delete penalty */
+        sched_yield(); /* delete penalty */
     }
     htsmsg_destroy(msg);