2019-11-15  Edward Smith-Rowland  <3dw4rd@verizon.net>

	Implement the default_searcher part of C++20 p1032 Misc constexpr bits.
	* include/std/functional
	(default_searcher, default_searcher::operator()): Constexpr.
	* testsuite/20_util/function_objects/constexpr_searcher.cc: New.

From-SVN: r278317