stl_algo.h (merge): Fix documentation.

stl_algo.h (merge): Fix documentation.

2019-09-28  François Dumont  <fdumont@gcc.gnu.org>

	* include/bits/stl_algo.h (merge): Fix documentation.
	* include/debug/functions.h (__check_sorted_aux): Add C++20 constexpr.
	(__check_sorted): Likewise and remove nested irreflexive check.
	(__check_sorted_set_aux, __check_sorted_set): Add C++20 constexpr.
	(__check_partitioned_lower, __check_partitioned_upper): Likewise.
	(_Irreflexive_checker::_S_is_valid): Likewise.
	(__is_irreflexive, __is_irreflexive_pred): Likewise.
	* include/debug/helper_functions.h (__get_distance): Add constexpr.
	(__valid_range_aux): Add C++20 constexpr.
	(__valid_range(_Iter, _Iter, _Distance_traits<_Iter>::__type&)):
	Likewise and add std::is_constant_evaluated check.
	(__valid_range_aux(_Iter, _Iter, std::input_iterator_tag)): New.
	(__valid_range_aux(_Iter, _Iter, std::random_accss_iterator_tag)): New.
	(__valid_range_aux(_Integral, _Integral, std::__true_type)): New,
	use latter.
	(__valid_range(_Iter, _Iter)): Adapt to use latter, add constexpr and
	__builtin_is_contant_evaludated check..
	(__can_advance, __base): Add constexpr.
	* include/debug/macros.h [_GLIBCXX_HAVE_BUILTIN_IS_CONSTANT_EVALUATED]
	(_GLIBCXX_DEBUG_VERIFY_COND_AT): New.
	(__glibcxx_check_sorted): Use __glibcxx_check_irreflexive.
	(__glibcxx_check_sorted_pred): Use __glibcxx_check_irreflexive_pred.
	* testsuite/25_algorithms/binary_search/constexpr.cc: Use irreflexive
	std::less.
	* testsuite/25_algorithms/is_sorted/constexpr.cc: Likewise.
	* testsuite/25_algorithms/merge/constexpr.cc: Fix order in camm. Fix
	lambda to be irreflexive.

From-SVN: r276260