Avoid matching type in huge-struct test error annotation

The concrete type that will be too big is target dependent. Avoid
matching it in error annotation to make test work correctly across
different targets.

src/test/ui/huge-struct.rs

@@ -47,6 +47,6 @@ struct S1M<T> { val: S1k<S1k<T>> }
 
 fn main() {
     let fat: Option<S1M<S1M<S1M<u32>>>> = None;
-    //~^ ERROR the type `S32<S1M<S1M<u32>>>` is too big for the current architecture
+    //~^ ERROR is too big for the current architecture
 
 }