re PR middle-end/50060 (intrinsics not folded by the middle-end)

re PR middle-end/50060 (intrinsics not folded by the middle-end)

	PR c++/50060
	* constexpr.c (cxx_eval_builtin_function_call): Pass false as lval
	when evaluating call arguments.  Use fold_builtin_call_array instead
	of fold_build_call_array_loc, return t if it returns NULL.  Otherwise
	check the result with potential_constant_expression and call
	cxx_eval_constant_expression on it.

	* g++.dg/cpp0x/constexpr-50060.C: New test.
	* g++.dg/cpp1y/constexpr-50060.C: New test.

From-SVN: r238520