Fix a couple of memory leaks in the C++ frontend

Fix a couple of memory leaks in the C++ frontend

The leak in get_mapped_args is due to auto_vec not properly supporting
destructible elements in that auto_vec's destructor doesn't call the
destructors of its elements.

gcc/cp/ChangeLog:

	* constraint.cc (get_mapped_args): Avoid using auto_vec
	as a vector element.  Release the vectors inside the lists
	vector.
	* parser.c (cp_literal_operator_id): Free the buffer.