GSB: Use the correct predicate to determine if a class uses Objective-C reference counting

I'm about to fix the same bug in the RequirementMachine, and to avoid spurious cross-checking
failures in -requirement-machine=verify mode, just fix this in the GSB as well.

Author: slavapestov

lib/AST/GenericSignatureBuilder.cpp

@@ -4494,7 +4494,7 @@ bool GenericSignatureBuilder::updateSuperclass(
 
     auto layout =
       LayoutConstraint::getLayoutConstraint(
-        superclass->getClassOrBoundGenericClass()->isObjC()
+        superclass->getClassOrBoundGenericClass()->usesObjCObjectModel()
           ? LayoutConstraintKind::Class
           : LayoutConstraintKind::NativeClass,
         getASTContext());