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

[Simon Pilgrim via llvm-commits]

RKSimon 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.......

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