* include/experimental/any (any): Remove allocator support and update
	feature-testing macro.
	* include/experimental/functional: Update feature-testing macro.
	* include/experimental/optional (optional::_M_get()): Add constexpr.
	(optional::operator*(), optional::value()): Overload and add
	ref-qualifiers. Update feature-testing macro.
	* include/experimental/string_view (basic_string_view::clear): Remove
	and update feature-testing macro.
	* testsuite/experimental/any/cons/3.cc: Remove.
	* testsuite/experimental/any/cons/4.cc: Remove.
	* testsuite/experimental/any/misc/any_cast.cc: Remove allocator tests.
	* testsuite/experimental/any/misc/any_cast_neg.cc: Adjust dg-error.
	* testsuite/experimental/string_view/capacity/1.cc: Don't test clear().

From-SVN: r218709