swift234

[ClangImporter] Prefer typedef sugar for blocks even in bridge-able contexts.

We'd rather show dispatch_async as

  // new
  func dispatch_async(queue: dispatch_queue_t!, block: dispatch_block_t!)

than

  // old
  func dispatch_async(queue: dispatch_queue_t!, block: (() -> Void)!)

which was only happening because we were trying to hide the @objc_block
annotation when possible. That's not necessary when we have a typealias.

<rdar://problem/16679280>

Swift SVN r17273