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

[Benjamin Maxwell via llvm-commits]

MacDue wrote:

> We've never made any progress vectorizing intrinsics with aggregate return types like this (e.g. overflow intrinsics)
> 
> @fhahn @alexey-bataev Do you think we can easily support this or should we consider alternatives? We've also had problems with handling arguments that take pointers (sincos / modf etc.) so I guess its just an annoying problem in general.......

I have a patch WIP patch to support this, I could share as a draft now.

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