[llvm] MathExtras: MulOverflow: use builtin when available (NFC) (PR #95046)

[Mehdi Amini via llvm-commits]

https://github.com/joker-eph approved this pull request.

Thanks for tracking this down!

Can we remove the ones that are in MLIR then?

https://github.com/llvm/llvm-project/pull/95046