Revert "Use CMAKE_RUNTIME_OUTPUT_DIRECTORY instead of LLVM_BINARY_DIR for installing Clang headers."
Revert "Use CMAKE_RUNTIME_OUTPUT_DIRECTORY instead of LLVM_BINARY_DIR for installing Clang headers."

This appears to be breaking the buildbots.

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@189426 91177308-0d34-0410-b5e6-96231b3b80d8

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