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

[Wenju He via cfe-commits]

wenju-he wrote:

> Checking the bitcode files look good to me, do you still see issues? Which library did you see the above discrepancy with?

thanks, no symbol missing now.

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