PR libstdc++/72745
	* include/std/array (get): Use positive message for static assertions.
	* include/std/functional (_Safe_tuple_element_t): Fix indentation.
	* include/std/tuple (tuple_element<I, tuple<>>): Add partial
	specialization for invalid indices, with static assertion.
	* testsuite/20_util/tuple/element_access/get_neg.cc: New test.

From-SVN: r238924