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_imp::do_deallocate): Add missing return.
	* testsuite/experimental/memory_resource/new_delete_resource.cc: New.
	* testsuite/experimental/memory_resource/resource_adaptor.cc: Test
	resource_adaptor with std::allocator, __gnu_cxx::new_allocator and
	__gnu_cxx::malloc_allocator.

From-SVN: r261851