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

[Wenju He via cfe-commits]

wenju-he wrote:

> 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.

Yes, you can concatenate multiple cache files. Different entries in these cache files will be combined. Override applies to same entries and the one in the last cache file wins.

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