PR libstdc++/70940 make pmr::resource_adaptor return aligned memory

PR libstdc++/70940 make pmr::resource_adaptor return aligned memory

	PR libstdc++/70940
	* include/experimental/memory_resource (__resource_adaptor_common):
	New base class.
	(__resource_adaptor_common::_AlignMgr): Helper for obtaining aligned
	pointer from unaligned, and vice versa.
	(__resource_adaptor_imp::do_allocate): Use _AlignMgr to adjust
	allocated pointer to meet alignment request.
	(__resource_adaptor_imp::do_deallocate): Use _AlignMgr to retrieve
	original pointer for deallocation.
	(__resource_adaptor_imp::do_is_equal): Reformat.
	(__resource_adaptor_imp::_S_aligned_size): Remove.
	(__resource_adaptor_imp::_S_supported): Remove.
	(new_delete_resource): Use __gnu_cxx::new_allocator.
	* testsuite/experimental/memory_resource/resource_adaptor.cc: Test
	extended alignments and use debug_allocator to check for matching
	allocate/deallocate pairs.

From-SVN: r261849