Make the filesystem::path constructors SFINAE away for void* arguments,
instead of giving an error due to iterator_traits<void*>::reference.

	PR libstdc++/90454.cc path construction from void*
	* include/bits/fs_path.h (path::_Path): Use remove_pointer so that
	pointers to void are rejected as well as void.
	* include/experimental/bits/fs_path.h (path::_Path): Likewise.
	* testsuite/27_io/filesystem/path/construct/80762.cc: Also check
	pointers to void.
	* testsuite/experimental/filesystem/path/construct/80762.cc: Likewise.

From-SVN: r271134