config: user: check for <aio.h>

And always zpool_read_label_slow() on non-conformant libcs

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Co-authored-by: José Luis Salvador Rufo <salvador.joseluis@gmail.com>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes #13207
Closes #13254

lib/libzutil/zutil_import.c

@@ -47,7 +47,9 @@
  * using our derived config, and record the results.
  */
 
+#ifdef HAVE_AIO_H
 #include <aio.h>
+#endif
 #include <ctype.h>
 #include <dirent.h>
 #include <errno.h>
@@ -982,6 +984,9 @@ zpool_read_label_slow(int fd, nvlist_t **config, int *num_labels)
 int
 zpool_read_label(int fd, nvlist_t **config, int *num_labels)
 {
+#ifndef HAVE_AIO_H
+	return (zpool_read_label_slow(fd, config, num_labels));
+#else
 	struct stat64 statbuf;
 	struct aiocb aiocbs[VDEV_LABELS];
 	struct aiocb *aiocbps[VDEV_LABELS];
@@ -1104,6 +1109,7 @@ zpool_read_label(int fd, nvlist_t **config, int *num_labels)
 	*config = expected_config;
 
 	return (0);
+#endif
 }
 
 /*