Bug#36867806 Heap-use-after-free: regexp::Regexp_facade::~Regexp_facade()

An SQL statement had heap-use-after-free when run as a prepared statement.
The failing statemen was a functional index in a create table statement,
and objects created ended up in the execution MEM_ROOT.

The solution is to switch to the prepare MEM_ROOT when doing resolving
of functional indexes.

Change-Id: Ic54ef5eaaa4b90e1018cb82b9c73f5f6c5e29e01

Author: Tor Didriksen

mysql-test/t/window_functions_bugs.test

@@ -1,4 +1,6 @@
 --source include/elide_costs.inc
+# difference in '$.steps[*].join_preparation.steps[*].'
+--source include/no_ps_protocol.inc
 
 --echo #
 --echo # Bug#26475312 VALGRIND MEMORY LEAK ( CMP_FIELD_VALUE(FIELD*, LONG) (SQL_EXECUTOR.CC:3598)

sql/sql_table.cc

@@ -8077,6 +8077,8 @@ static Create_field *add_functional_index_to_create_list(
     const Functional_index_error_handler error_handler(
         {key_spec->name.str, key_spec->name.length}, thd);
 
+    const Prepared_stmt_arena_holder ps_arena_holder(thd);
+
     Item *expr = kp->get_expression();
     if (expr->type() == Item::FIELD_ITEM) {
       my_error(ER_FUNCTIONAL_INDEX_ON_FIELD, MYF(0));