PR c++/56041
	* cp-tree.h (struct processing_template_decl_sentinel): New.
	* pt.c (instantiate_non_dependent_expr_internal): Split out from...
	(instantiate_non_dependent_expr_sfinae): Here.
	(convert_nontype_argument): Use them.
	* constexpr.c (fold_non_dependent_expr): Use them.

From-SVN: r217823