MDEV-17813: Fix the test for release builds

mysql-test/suite/innodb/r/instant_alter_purge,release.rdiff

+--- instant_alter_purge.result
++++ instant_alter_purge,release.result
+@@ -32,15 +32,11 @@
+ START TRANSACTION WITH CONSISTENT SNAPSHOT;
+ connection default;
+ DELETE FROM t1;
+-SET DEBUG_SYNC='innodb_commit_inplace_alter_table_enter SIGNAL go WAIT_FOR do';
+ ALTER TABLE t1 ADD COLUMN f3 INT;
+ connection purge_control;
+-SET DEBUG_SYNC='now WAIT_FOR go';
+ COMMIT;
+ InnoDB		0 transactions not purged
+-SET DEBUG_SYNC='now SIGNAL do';
+ disconnect purge_control;
+ connection default;
+-SET DEBUG_SYNC=RESET;
+ DROP TABLE t1;
+ SET GLOBAL innodb_purge_rseg_truncate_frequency = @saved_frequency;

mysql-test/suite/innodb/t/instant_alter_purge.test

 --source include/have_innodb.inc
+--source include/maybe_debug.inc
+if ($have_debug) {
+--source include/have_debug_sync.inc
+}
 
 SET @saved_frequency = @@GLOBAL.innodb_purge_rseg_truncate_frequency;
 SET GLOBAL innodb_purge_rseg_truncate_frequency=1;
@@ -45,19 +49,27 @@ START TRANSACTION WITH CONSISTENT SNAPSHOT;
 connection default;
 DELETE FROM t1;
 
+if ($have_debug) {
 SET DEBUG_SYNC='innodb_commit_inplace_alter_table_enter SIGNAL go WAIT_FOR do';
+}
 send ALTER TABLE t1 ADD COLUMN f3 INT;
 
 connection purge_control;
+if ($have_debug) {
 SET DEBUG_SYNC='now WAIT_FOR go';
+}
 COMMIT;
 --source include/wait_all_purged.inc
+if ($have_debug) {
 SET DEBUG_SYNC='now SIGNAL do';
+}
 disconnect purge_control;
 
 connection default;
 reap;
+if ($have_debug) {
 SET DEBUG_SYNC=RESET;
+}
 DROP TABLE t1;
 
 SET GLOBAL innodb_purge_rseg_truncate_frequency = @saved_frequency;