re PR c++/88866 (g++.dg/cpp0x/variadic126.C fails with -std=c++2a)

	PR c++/88866
	* g++.dg/cpp0x/variadic126.C: Tweak dg-error.

From-SVN: r267944

gcc/testsuite/ChangeLog

+2019-01-15  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/88866
+	* g++.dg/cpp0x/variadic126.C: Tweak dg-error.
+
 2019-01-15  Richard Sandiford  <richard.sandiford@arm.com>
 
 	PR inline-asm/52813

gcc/testsuite/g++.dg/cpp0x/variadic126.C

@@ -3,6 +3,6 @@
 
 template < typename ... > struct A;
 
-struct B : A <			// { dg-error "invalid" }
+struct B : A <			// { dg-error "invalid" "" { target c++17_down } }
 {
-};
+}; // { dg-error "mismatch|expected" "" { target c++2a } }