re PR c++/92869 (C++17 wrongly reports aggregate type as not-aggregate (when explicitly defaulted ctors are added))

	PR c++/92869
	* class.c (finish_struct): For C++17 and earlier, check
	type_has_user_provided_or_explicit_constructor rather than
	TYPE_HAS_USER_CONSTRUCTOR whether to set CLASSTYPE_NON_AGGREGATE.

	* g++.dg/cpp0x/aggr3.C: New test.

From-SVN: r279241