swift234

[ClangImporter] Generalize the hack from r29212 to cover any unavailable members.

If there is a method -foo: that's unavailable (for whatever reason), and we now
have a method -foo:error: that we'd like to import, it's okay to drop the error
parameter there. Overload resolution can handle filtering out the unavailable
method.

rdar://problem/21497221

Swift SVN r29746