Fix failing tests

Author: Manishearth

src/test/compile-fail/object-lifetime-default.rs

@@ -8,6 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#![feature(rustc_attrs)]
+
 #[rustc_object_lifetime_default]
 struct A<T>(T); //~ ERROR None
 

src/test/compile-fail/region-object-lifetime-1.rs

@@ -11,6 +11,7 @@
 // Various tests related to testing how region inference works
 // with respect to the object receivers.
 
+#![feature(rustc_attrs)]
 #![allow(warnings)]
 
 trait Foo {

src/test/compile-fail/region-object-lifetime-3.rs

@@ -11,6 +11,7 @@
 // Various tests related to testing how region inference works
 // with respect to the object receivers.
 
+#![feature(rustc_attrs)]
 #![allow(warnings)]
 
 trait Foo {