zdb: ASSERT issues when DEBUG is not defined

If zdb is not built with DEBUG mode, the ASSERT macros will be
eliminated.

This will leave vim defined, but not used (gcc warning) and
checkpoint spacemap validation loop will do nothing.

Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: Toomas Soome <[email protected]>
Closes #11932

Author: tsoome

cmd/zdb/zdb.c

@@ -5840,7 +5840,8 @@ zdb_leak_init_prepare_indirect_vdevs(spa_t *spa, zdb_cb_t *zcb)
 		 */
 		VERIFY0(vdev_metaslab_init(vd, 0));
 
-		vdev_indirect_mapping_t *vim = vd->vdev_indirect_mapping;
+		vdev_indirect_mapping_t *vim __maybe_unused =
+		    vd->vdev_indirect_mapping;
 		uint64_t vim_idx = 0;
 		for (uint64_t m = 0; m < vd->vdev_ms_count; m++) {
 
@@ -6933,7 +6934,7 @@ verify_checkpoint_vdev_spacemaps(spa_t *checkpoint, spa_t *current)
 		for (uint64_t c = ckpoint_rvd->vdev_children;
 		    c < current_rvd->vdev_children; c++) {
 			vdev_t *current_vd = current_rvd->vdev_child[c];
-			ASSERT3P(current_vd->vdev_checkpoint_sm, ==, NULL);
+			VERIFY3P(current_vd->vdev_checkpoint_sm, ==, NULL);
 		}
 	}