libstdc++: Simplify std::any to fix -Wdeprecated-declarations warning

We don't need to use std::aligned_storage in std::any. We just need a
POD type of the right size. The void* union member already ensures the
alignment will be correct. Avoiding std::aligned_storage means we don't
need to suppress a -Wdeprecated-declarations warning.

libstdc++-v3/ChangeLog:

	* include/experimental/any (experimental::any::_Storage): Use
	array of unsigned char instead of deprecated
	std::aligned_storage.
	* include/std/any (any::_Storage): Likewise.
	* testsuite/20_util/any/layout.cc: New test.