re PR c++/47774 ([C++0x] constexpr specifier on ctor not ignored when template instantiation causes ctor to not satify constexpr requirements)

	PR c++/47774
	* tree.c (build_vec_init_elt): Split out from...
	(build_vec_init_expr): ...here.
	(diagnose_non_constexpr_vec_init): New fn.
	* semantics.c (potential_constant_expression_1): Use it.
	* cp-tree.h: Declare it.

From-SVN: r170638