PR c++/57550
	* pt.c (fn_type_unification): Only defer during substitution.
	(type_unification_real): Defer during defarg substitution,
	add checks parm to pass back deferred checks.
	(unify, do_auto_deduction): Adjust.
	* semantics.c (reopen_deferring_access_checks): New.
	* cp-tree.h: Declare it.

From-SVN: r200808