PR libstdc++/90220 Fix any_cast for non-object types

PR libstdc++/90220 Fix any_cast for non-object types

Backport from mainline
2019-04-24  Jonathan Wakely  <jwakely@redhat.com>

	PR libstdc++/90220 (partial)
	* include/std/any (any_cast<T>(any*), any_cast<T>(const any*)): Do
	not attempt ill-formed static_cast to pointers to non-object types.
	* testsuite/20_util/any/misc/any_cast.cc: Test std::any_cast with
	function types.

Backport from mainline
2019-04-24  Jonathan Wakely  <jwakely@redhat.com>

	PR libstdc++/90220
	* include/std/any (__any_caster): Use remove_cv_t instead of decay_t.
	Avoid a runtime check for types that can never be stored in std::any.
	* testsuite/20_util/any/misc/any_cast.cc: Test std::any_cast with
	array types.

Backport from mainline
2019-05-23  Jonathan Wakely  <jwakely@redhat.com>

	PR libstdc++/90220
	* include/experimental/any (__any_caster): Constrain to only be
	callable for object types. Use remove_cv_t instead of decay_t.
	If the type decays or isn't copy constructible, compare the manager
	function to a dummy specialization.
	(__any_caster): Add overload constrained for non-object types.
	(any::_Manager_internal<_Op>): Add dummy specialization.
	* testsuite/experimental/any/misc/any_cast.cc: Test function types
	and array types.

From-SVN: r271565