swift234

Fix broken tests due to oversight

After latest set of fixes I only ran the tests on iPhone, which disables
the IRGen test. Ugh...

- r29261 removed an IBAction check in requiresObjCMethodDescriptor() --
  turns out the IBAction attribute does not imply @objc, so this was
  wrong.

- r29263 needed a test update for @nonobjc override semantics.

Swift SVN r29265