[CMake] clang/lib: Prune redundant dependencies.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@196864 91177308-0d34-0410-b5e6-96231b3b80d8
Revert r196859, "Use llvm::sys::path::append to concatenate paths", to appease FileManager.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@196865 91177308-0d34-0410-b5e6-96231b3b80d8