[libclc] [libclc] Use custom CMake handling to overhaul libclc compilation (PR #185247)

[Matt Arsenault via cfe-commits]

arsenm wrote:

Also why is this being packaged in lib64? This should only really go in the clang resource directory. This isn't really usable as a standalone project 

https://github.com/llvm/llvm-project/pull/185247