[CMake] Add missing set_output_directory after Takumi's change in r198205.
[CMake] Add missing set_output_directory after Takumi's change in r198205.

In a standalone build, Clang binaries should end up in Clang's build folder,
not LLVM's.

Xcode still has a few issues finding auxiliary tools and libraries in the
build folders. I'll fix those next.

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@198328 91177308-0d34-0410-b5e6-96231b3b80d8

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