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

[Benjamin Maxwell via llvm-commits]

MacDue wrote:

Note: This is part of https://discourse.llvm.org/t/rfc-add-struct-returning-intrinsics-for-math-functions-with-output-pointers/81164

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