Implement P0032R3, Homogeneous interface for variant, any and optional,

Implement P0032R3, Homogeneous interface for variant, any and optional,

	for the parts concerning any and optional.
	* include/std/any (_Storage()): Make constexpr and have it
	initialize _M_ptr.
	(any()): Make constexpr.
	(any(const any&)): Adjust.
	(any(any&&)): Likewise.
	(__any_constructible_t): New.
	(any(_ValueType&&)): Constrain.
	(any(in_place_type_t<_Tp>, _Args&&...)): New.
	(any(in_place_type_t<_Tp>, initializer_list<_Up>, _Args&&...)):
	Likewise.
	(~any()): Adjust.
	(operator=(const any&)): Likewise.
	(operator=(any&&)): Likewise.
	(operator=(_ValueType&&)): Constrain.
	(emplace(_Args&&...)): New.
	(emplace(initializer_list<_Up>, _Args&&...)): Likewise.
	(clear()): Remove.
	(reset()): New.
	(swap(any&)): Adjust.
	(empty()): Remove.
	(has_value()): New.
	(type()): Adjust.
	(_Manager_internal::_S_create(_Storage&, _Args&&...)): New.
	(_Manager_external::_S_create(_Storage&, _Args&&...)): Likewise.
	(make_any(_Args&&...)): Likewise.
	(make_any(initializer_list<_Up>, _Args&&...)): Likewise.
	* include/std/optional (in_place_t, in_place): Remove.
	(bad_optional_access): Add a comment referring to LEWG 72.
	(emplace(_Args&&...)): Constrain.
	(has_value()): New.
	(reset()): Likewise.
	(make_optional(_Args&&...)): Likewise.
	(make_optional(initializer_list<_Up>, _Args&&...)): Likewise.
	* include/std/utility (in_place_tag): New.
	(__in_place, __in_place_type, __in_place_index): Likewise.
	(in_place_t, in_place_type_t, in_place_index_t): Likewise.
	(in_place(__in_place*)): Likewise.
	(in_place(__in_place_type<_Tp>*)): Likewise.
	(in_place(__in_place_index<_Idx>*)): Likewise.
	* testsuite/20_util/any/assign/1.cc: Adjust.
	* testsuite/20_util/any/assign/emplace.cc: New.
	* testsuite/20_util/any/assign/self.cc: Adjust.
	* testsuite/20_util/any/cons/1.cc: Likewise.
	* testsuite/20_util/any/cons/in_place.cc: New.
	* testsuite/20_util/any/make_any.cc: Likewise.
	* testsuite/20_util/any/misc/any_cast_neg.cc: Adjust.
	* testsuite/20_util/any/misc/swap.cc: Likewise.
	* testsuite/20_util/any/modifiers/1.cc: Likewise.
	* testsuite/20_util/any/requirements.cc: New.
	* testsuite/20_util/in_place/requirements.cc: Likewise.
	* testsuite/20_util/optional/constexpr/in_place.cc: Adjust.
	* testsuite/20_util/optional/in_place.cc: Likewise.
	* testsuite/20_util/optional/make_optional.cc: Add tests for
	the new overloads of make_optional.

From-SVN: r238329