We add a new clang library called `clangSupport` for putting those utils which can be used in clang table-gen and other clang component.
We tried to put that into `llvm/Support`, but actually those stuffs only used in clang* and clang-tblgen, so I think that might be better to create `clang/Support`
* clang will used that in https://reviews.llvm.org/D111617.
Reviewed By: khchen, MaskRay, aaron.ballman
Differential Revision: https://reviews.llvm.org/D121984
Kito Cheng