PR67085 pass comparison functions by reference in heap algorithms

PR67085 pass comparison functions by reference in heap algorithms

	PR libstdc++/67085
	* include/bits/predefined_ops.h (_Iter_less_val, _Val_less_iter): Add
	converting constructors from _Iter_less_iter.
	(_Iter_comp_val, _Val_comp_iter): Add converting constructors from
	_Iter_comp_iter.
	(__iter_comp_val(_Iter_comp_iter<C>): Use converting constructor.
	(__val_comp_iter(_Iter_comp_iter<C>): Likewise.
	* include/bits/stl_heap.h (__is_heap_until, __push_heap, __pop_heap)
	(__make_heap, __sort_heap): Change _Compare parameters to references.
	(__is_heap, push_heap, __adjust_heap, __pop_heap, pop_heap)
	(__make_heap, make_heap, sort_heap, is_heap_until): Pass comparison
	functions as lvalues.
	(is_heap): Call __is_heap_until directly to avoid copying __comp.
	* testsuite/23_containers/priority_queue/67085.cc: Adjust test to
	count copies during construction with empty sequence.

From-SVN: r244656