[llvm] [LoopVectorize] Refine runtime memory check costs when there is an outer loop (PR #76034)

[Florian Hahn via llvm-commits]

fhahn wrote:

> > Could you update the places that look up the outer loop to use the new variable as well?
> 
> Hi @fhahn, I couldn't find any other instances in GeneratedRTChecks where we call `getParentLoop()`. I'm not sure where else I could use `OuterLoop`?

There are 2 places that do something like `if (auto *PL = LI->getLoopFor(LoopVectorPreHeader)...`, which effectively checks if there's an outer loop

https://github.com/llvm/llvm-project/pull/76034