BUG#18037: Fix stack corruption in THD::rollback_item_tree_changes().

  
Stored procedure execution sometimes placed the address of auto variables
in the list of Item changes to undo in THD::rollback_item_tree_changes().
This could cause stack corruption.


sql/sp_head.cc:
  Avoid storing address of auto variables in global rollback list, to
  prevent stack memory corruption.
sql/sp_head.h:
  Avoid storing address of auto variables in global rollback list, to
  prevent stack memory corruption.
sql/sp_rcontext.cc:
  Avoid storing address of auto variables in global rollback list, to
  prevent stack memory corruption.
sql/sp_rcontext.h:
  Avoid storing address of auto variables in global rollback list, to
  prevent stack memory corruption.
sql/sql_class.cc:
  Avoid storing address of auto variables in global rollback list, to
  prevent stack memory corruption.