This fixes a test failure with -D_GLIBCXX_DEBUG:

FAIL: 23_containers/array/comparison_operators/constexpr.cc (test for excess errors)

	* include/debug/array (operator<=>): Define for C++20.
	* testsuite/23_containers/array/tuple_interface/get_debug_neg.cc:
	Adjust dg-error line numbers.
	* testsuite/23_containers/array/tuple_interface/
	tuple_element_debug_neg.cc: Likewise.