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

[Thorsten Schütt via llvm-commits]

tschuett wrote:

We commonly add a test when importing a new intrinsics: https://github.com/llvm/llvm-project/pull/88240.
We have for the first time in a while an intrinsic which returns two values. A test would be nice to have to make sure we got everything right.

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