PR c++/68782

gcc/
	* tree.c (recompute_constructor_flags): Split out from
	build_constructor.
	(verify_constructor_flags): New.
	* tree.h: Declare them.
gcc/cp/
	* constexpr.c (cxx_eval_bare_aggregate): Update TREE_CONSTANT
	and TREE_SIDE_EFFECTS.
	(cxx_eval_constant_expression) [CONSTRUCTOR]: Call
	verify_constructor_flags.

From-SVN: r232847