class.c (trivial_default_constructor_is_constexpr): Rename from synthesized_default_constructor_is_constexpr.

	* class.c (trivial_default_constructor_is_constexpr): Rename from
	synthesized_default_constructor_is_constexpr.
	(type_has_constexpr_default_constructor): Adjust.
	(add_implicitly_declared_members): Call it instead.
	(explain_non_literal_class): Explain about non-constexpr default ctor.
	* cp-tree.h: Adjust.
	* method.c (synthesized_method_walk): Adjust.
	* semantics.c (explain_invalid_constexpr_fn): Handle defaulted
	functions, too.

From-SVN: r178519