swift234

When loading a Swift framework module, see if it's also a Clang module.

In a framework containing both Clang headers and a Swift module, the Swift
module gets picked up first, but then automatically imports (and re-exports)
the Clang module as well.

One interesting case here is that it's possible for the Clang side to add
categories to a class declared in Swift. In order to support this, the
Clang importer can now find extensions for Swift classes marked @objc.
(I couldn't think of a way to test this separately; the previous commit
was supposed to do that, but worked without this change.)

<rdar://problem/16295937>

Swift SVN r15084