Missing unchecked cast warning in polymorphic method call

[stephan-herrmann]

Ecj exhibits the same bug that javac < 24 did:

 import java.lang.invoke.VarHandle;
class VarHandleCast<V> {
     VarHandle vh;
     V method(Object obj) {
         return (V)vh.getAndSet(this, obj);
     }
} 

this should trigger an unchecked cast warning, but doesn't.

See https://bugs.openjdk.org/browse/JDK-8343286