[llvm] [LV][NFCI]Use integer for cost/trip count calculations instead of double, fix possible UB. (PR #87241)

[Florian Hahn via llvm-commits]

fhahn wrote:

Thanks for splitting this off. Could you add a test case that exposes the UBSan failure w/o this patch?

https://github.com/llvm/llvm-project/pull/87241