Some more C++20 changes from P1614R2, "The Mothership has Landed".

	* include/bits/stl_queue.h (queue): Define operator<=> for C++20.
	* include/bits/stl_stack.h (stack): Likewise.
	* testsuite/23_containers/queue/cmp_c++20.cc: New test.
	* testsuite/23_containers/stack/cmp_c++20.cc: New test.