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

module/zfs/vdev_rebuild.c

@@ -260,7 +260,7 @@ vdev_rebuild_initiate_sync(void *arg, dmu_tx_t *tx)
 }
 
 static void
-vdev_rebuild_log_notify(spa_t *spa, vdev_t *vd, char *name)
+vdev_rebuild_log_notify(spa_t *spa, vdev_t *vd, const char *name)
 {
 	nvlist_t *aux = fnvlist_alloc();