on failed aio submission, set aiocb error and return value

it's not clear whether this is required, but it seems arguable that it
should happen. for example aio_suspend is supposed to return
immediately if any of the operations has "completed", which includes
ending with an error status asynchonously and might also be
interpreted to include doing so synchronously.

src/aio/aio.c

@@ -280,6 +280,8 @@ static int submit(struct aiocb *cb, int op)
 
 	if (!q) {
 		if (errno != EBADF) errno = EAGAIN;
+		cb->__ret = -1;
+		cb->__err = errno;
 		return -1;
 	}
 	q->ref++;
@@ -303,8 +305,8 @@ static int submit(struct aiocb *cb, int op)
 	if (pthread_create(&td, &a, io_thread_func, &args)) {
 		pthread_mutex_lock(&q->lock);
 		__aio_unref_queue(q);
-		errno = EAGAIN;
-		ret = -1;
+		cb->__err = errno = EAGAIN;
+		cb->__ret = ret = -1;
 	}
 	pthread_sigmask(SIG_SETMASK, &origmask, 0);