[llvm] [IRBuilder] Fold binary intrinsics (PR #80743)

[Nikita Popov via llvm-commits]

nikic wrote:

It's not possible to use it in ConstantFolder, but you can use it in TargetFolder. We could try to move parts of it into IR, but I don't think that's worthwhile (it would be easier to switch SLP to use TargetFolder).

https://github.com/llvm/llvm-project/pull/80743