PR c++/77553
	* constexpr.c (cxx_fold_pointer_plus_expression): New function.
	(cxx_eval_binary_expression): Use it for POINTER_PLUS_EXPR.
	(cxx_eval_pointer_plus_expression): Remove.
	(cxx_eval_constant_expression) <case POINTER_PLUS_EXPR>: Don't
	call cxx_eval_pointer_plus_expression.

	* g++.dg/cpp1y/constexpr-77553.C: New test.

From-SVN: r240119