swift234

Sema: Your monthly dose of minor @objc fixes

- Disallow @objc on members of non-@objc protocols (the
  real reason for this patch)

- Add a separate diagnostic for @objc appearing on members
  in non-class, non-protocol types.

- Clean up the code that enforces that @objc can only be
  applied to @objc-rooted classes. The diagnostic would
  be incorrectly emitted for @objc subclasses of generic
  classes.

Fixes <rdar://problem/17273524>.

Swift SVN r31303