Problem is due to missing implementation of
Item_func_make_set::fix_after_pullout(), which makes this particular
MAKE_SET function be regarded as const and may thus be evaluated
during resolving.

Fixed by implementing a proper fix_after_pullout() function.

Change-Id: I7094869588ce4133c4a925e1a237a37866a5bb3c
(cherry picked from commit a9f0b388adeef837811fdba2bce2e4ba5b06863b)