[CMake] One more stab at fixing BUILD_SHARED_LIBS
[CMake] One more stab at fixing BUILD_SHARED_LIBS

If clang's libraries are build SHARED, we need to grab their `PRIVATE_LINK_LIBRARIES` properties and add those to clang_shared's interface.

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@361275 91177308-0d34-0410-b5e6-96231b3b80d8

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