c++: address of class NTTP object as targ [PR113242]

c++: address of class NTTP object as targ [PR113242]

invalid_tparm_referent_p was rejecting using the address of a class NTTP
object as a template argument, but this should be fine.

	PR c++/113242
	PR c++/99493

gcc/cp/ChangeLog:

	* pt.cc (invalid_tparm_referent_p) <case ADDR_EXPR>: Suppress
	DECL_ARTIFICIAL rejection test for class NTTP objects.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp2a/nontype-class61.C: New test.
	* g++.dg/cpp2a/nontype-class62.C: New test.

Reviewed-by: Jason Merrill <jason@redhat.com>
(cherry picked from commit 68cea2d32a9fd525154b6a48042e5835d4c5e371)