Reimplement ExternalSemaSource delegation in terms of MultiplexExternalSemaSource to remove one of the places that needs updating every time the ExternalSemaSource interface changes.
Reimplement ExternalSemaSource delegation in terms of
MultiplexExternalSemaSource to remove one of the places that needs updating
every time the ExternalSemaSource interface changes.


git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@275653 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang