Another test whose diagnostics improved

Author: DougGregor

test/Generics/existential_restrictions.swift

@@ -53,17 +53,17 @@ class GP<T : P> {}
 class GOP<T : OP> {}
 class GCP<T : CP> {}
 class GSP<T : SP> {}
-class GAO<T : AnyObject> {}
+class GAO<T : AnyObject> {} // expected-note 2{{requirement specified as 'T' : 'AnyObject'}}
 
 func blackHole(_ t: Any) {}
 
 func testBindExistential() {
   blackHole(GP<P>()) // expected-error{{using 'P' as a concrete type conforming to protocol 'P' is not supported}}
   blackHole(GOP<OP>())
   blackHole(GCP<CP>()) // expected-error{{using 'CP' as a concrete type conforming to protocol 'CP' is not supported}}
-  blackHole(GAO<P>()) // expected-error{{'P' is not convertible to 'AnyObject'}}
+  blackHole(GAO<P>()) // expected-error{{'GAO' requires that 'P' be a class type}}
   blackHole(GAO<OP>())
-  blackHole(GAO<CP>()) // expected-error{{'CP' is not convertible to 'AnyObject'}}
+  blackHole(GAO<CP>()) // expected-error{{'GAO' requires that 'CP' be a class type}}
   blackHole(GSP<SP>()) // expected-error{{'SP' cannot be used as a type conforming to protocol 'SP' because 'SP' has static requirements}}
   blackHole(GAO<AnyObject>())
 }