[libclc] [libclc] Optimize ceil/fabs/floor/rint/trunc (PR #119596)

[Matt Arsenault via cfe-commits]

https://github.com/arsenm approved this pull request.

LGTM. I'm not sure how this all ends up expanding, I was expecting to see the elementwise builtins used.

It would be great if we had update_cc_test_checks style testing for the resulting implementation 

https://github.com/llvm/llvm-project/pull/119596