Extend debug_assert_on_not_freed_memory

Don't check global_memory_used if
debug_assert_on_not_freed_memory is not set

sql/mysqld.cc

@@ -2169,7 +2169,8 @@ static void mysqld_exit(int exit_code)
   if (opt_endinfo && global_status_var.global_memory_used)
     fprintf(stderr, "Warning: Memory not freed: %ld\n",
             (long) global_status_var.global_memory_used);
-  if (!opt_debugging && !my_disable_leak_check && exit_code == 0)
+  if (!opt_debugging && !my_disable_leak_check && exit_code == 0 &&
+      debug_assert_on_not_freed_memory)
   {
     DBUG_ASSERT(global_status_var.global_memory_used == 0);
   }