[libclc] [libclc][CMake] Add cmake cache files (PR #201480)

[Konrad Kleine via cfe-commits]

kwk wrote:

We don't use them (at least for now) when building libclc with all the rest of llvm. But I would like to understand if one can use multiple cache files from multiple projects as in `cmake -C libclc/cmake/caches/amdgcn-amd-amdhsa-llvm.cmake -C <otherproject>/cmake/caches/foo.cmake` and overwrite stuff like `LLVM_ENABLE_PROJECTS` for example after the fact.

https://github.com/llvm/llvm-project/pull/201480