re PR c++/45923 (constexpr diagnostics, more more)

re PR c++/45923 (constexpr diagnostics, more more)

	PR c++/45923
	* class.c (explain_non_literal_class): New.
	(finalize_literal_type_property): Call it.
	* cp-tree.h: Declare it.
	* semantics.c (ensure_literal_type_for_constexpr_object): Call it.
	(is_valid_constexpr_fn): Likewise.
	(massage_constexpr_body): Split out from...
	(register_constexpr_fundef): ...here.
	(is_instantiation_of_constexpr): New.
	(expand_or_defer_fn_1): Leave DECL_SAVED_TREE alone in that case.
	(explain_invalid_constexpr_fn): New.
	(cxx_eval_call_expression): Call it.
	(potential_constant_expression_1): Likewise.  Avoid redundant errors.
	* method.c (process_subob_fn): Diagnose non-constexpr.
	(walk_field_subobs): Likewise.
	(synthesized_method_walk): Don't shortcut if we want diagnostics.
	(explain_implicit_non_constexpr): New.
	(defaulted_late_check): Use it.
	* call.c (build_cxx_call): Remember location.

From-SVN: r175646