[libclc] [libclc] use default paths with find_program when possible (PR #105969)

[Fraser Cormack via cfe-commits]

frasercrmck wrote:

> > Nixpkgs has no intention of moving away from standalone builds.
> 
> I encourage you to acquire that intention. IMO libclc should not support the standalone build, and this should be version locked to the exact compiler commit. It's compiler data, not a real library

I don't disagree. The standalone builds are never going to be well tested and imo are a considerable barrier to (confidently) improving libclc. I know we've discussed this in the past.

That said, I'm not sure what the best course of action is. Would we be best to deprecate standalone builds in the next release, then drop them afterwards? Do we need an RFC? Do we need documentation for users on how to find the "archived" standalone build support if they wanted it?

https://github.com/llvm/llvm-project/pull/105969