[llvm] [IR] Add `llvm.sincos` intrinsic (PR #109825)

[Sander de Smalen via llvm-commits]

https://github.com/sdesmalen-arm commented:

This intrinsic and the reason for having it makes sense to me. The code looks fine too, only left a few minor comments.

https://github.com/llvm/llvm-project/pull/109825