Enable -Wwrite-strings

Also, fix leak from ztest_global_vars_to_zdb_args()

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes #13348

lib/libzutil/os/linux/zutil_import_os.c

@@ -328,7 +328,9 @@ zpool_find_import_blkid(libpc_handle_t *hdl, pthread_mutex_t *lock,
 		return (EINVAL);
 	}
 
-	error = blkid_dev_set_search(iter, "TYPE", "zfs_member");
+	/* Only const char *s since 2.32 */
+	error = blkid_dev_set_search(iter,
+	    (char *)"TYPE", (char *)"zfs_member");
 	if (error != 0) {
 		blkid_dev_iterate_end(iter);
 		blkid_put_cache(cache);

lib/libzutil/zutil_import.c

@@ -1543,7 +1543,7 @@ discover_cached_paths(libpc_handle_t *hdl, nvlist_t *nv,
 	 */
 	if (nvlist_lookup_string(nv, ZPOOL_CONFIG_PATH, &path) == 0) {
 		if ((dl = zfs_dirnamelen(path)) == -1)
-			path = ".";
+			path = (char *)".";
 		else
 			path[dl] = '\0';
 		return (zpool_find_import_scan_dir(hdl, lock, cache,