MDEV-33768: Memory leak found in the test main.constraints run with...

MDEV-33768: Memory leak found in the test main.constraints run with --ps-protocol against a server built with the option -DWITH_PROTECT_STATEMENT_MEMROOT

The discovered memory leak was introduced by the commit
  762bf7a0
    (MDEV-22602 Disable UPDATE CASCADE for SQL constraints)

The reason why a memory leaked on running the test main.constraints
is that a statement arena was used for allocation a memory
for storing a constraint name. A constraint name is an entity having
temporary nature by its design so runtime arena should be used for its
allocation.

mysql-test/main/constraints.result

@@ -235,3 +235,16 @@ t1	CREATE TABLE `t1` (
 ) ENGINE=MyISAM DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci
 drop procedure sp;
 drop table t1;
+#
+# MDEV-33768: Memory leak found in the test main.constraints run with --ps-protocol against a server built with the option -DWITH_PROTECT_STATEMENT_MEMROOT
+# This test case was added by reviewer's request.
+#
+PREPARE stmt FROM 'CREATE TABLE t1 (a INT)';
+EXECUTE stmt;
+DROP TABLE t1;
+EXECUTE stmt;
+EXECUTE stmt;
+ERROR 42S01: Table 't1' already exists
+# Clean up
+DROP TABLE t1;
+DEALLOCATE PREPARE stmt;

mysql-test/main/constraints.test

@@ -189,3 +189,18 @@ call sp;
 show create table t1;
 drop procedure sp;
 drop table t1;
+
+--echo #
+--echo # MDEV-33768: Memory leak found in the test main.constraints run with --ps-protocol against a server built with the option -DWITH_PROTECT_STATEMENT_MEMROOT
+--echo # This test case was added by reviewer's request.
+--echo #
+PREPARE stmt FROM 'CREATE TABLE t1 (a INT)';
+EXECUTE stmt;
+DROP TABLE t1;
+EXECUTE stmt;
+--error ER_TABLE_EXISTS_ERROR
+EXECUTE stmt;
+
+--echo # Clean up
+DROP TABLE t1;
+DEALLOCATE PREPARE stmt;

sql/sql_table.cc

@@ -5861,7 +5861,8 @@ static bool make_unique_constraint_name(THD *thd, LEX_CSTRING *name,
     if (!check)                                 // Found unique name
     {
       name->length= (size_t) (real_end - buff);
-      name->str= strmake_root(thd->stmt_arena->mem_root, buff, name->length);
+      name->str= thd->strmake(buff, name->length);
+
       return (name->str == NULL);
     }
   }