c++: decltype of non-dependent call of class type [PR105386]

We need to pass tf_decltype when instantiating a non-dependent decltype
operand, like tsubst does in the dependent case, so that we don't force
completion of a prvalue operand's class type.

	PR c++/105386

gcc/cp/ChangeLog:

	* semantics.cc (finish_decltype_type): Pass tf_decltype to
	instantiate_non_dependent_expr_sfinae.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/decltype81.C: New test.

gcc/cp/semantics.cc

@@ -11252,7 +11252,7 @@ finish_decltype_type (tree expr, bool id_expression_or_member_access_p,
     }
   else if (processing_template_decl)
     {
-      expr = instantiate_non_dependent_expr_sfinae (expr, complain);
+      expr = instantiate_non_dependent_expr_sfinae (expr, complain|tf_decltype);
       if (expr == error_mark_node)
 	return error_mark_node;
       /* Keep processing_template_decl cleared for the rest of the function

gcc/testsuite/g++.dg/cpp0x/decltype81.C

@@ -0,0 +1,15 @@
+// PR c++/105386
+// { dg-do compile { target c++11 } }
+
+template<class T> struct NoInst {
+  static_assert(sizeof(T) == 9999, "NoInst instantiated");
+};
+
+template<class T> NoInst<T> f(T);
+
+template<class>
+struct A {
+  using type = decltype(f(0));
+};
+
+A<int> a;