swift234

IRGen: Consistently mangle protocol names in protocol descriptors with the _Tt prefix.

Since protocol descriptors look like ObjC Protocol objects, we want to mangle the type prefix into their names to make them obviously Swift mangled names, but we were only doing this for @objc protocols, not native protocols. For consistency, do the same thing with native descriptors, and update the runtime type display code to match. Fixes rdar://problem/19691574.

Swift SVN r25014