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

[Joseph Huber via cfe-commits]

jhuber6 wrote:

Thanks for the reviews, hopefully this doesn't break anything. It kind of removes the device handling, but I don't know if that was actually functioning as intended anyway. We'll probably need to augment this with some new libraries for actual target specific stuff.

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