[llvm] [ConstantFolding] Constant fold nextafter and nexttoward (PR #168794)

[Sayan Sivakumaran via llvm-commits]

sivakusayan wrote:

@arsenm Thanks for the next round of review - I'll get to this sometime this weekend and implement the suggested changes. I'll probably need to rebase since this branch is a bit stale.

https://github.com/llvm/llvm-project/pull/168794