[llvm] [LV] Use shl for (VFxUF * vscale) when creating minimum iter check. (PR #153495)

[Luke Lau via llvm-commits]

https://github.com/lukel97 commented:

Could we also get the same thing if we instantiate the IRBuilder above with `IRBuilder<InstSimplifyFolder>`? I presume if it's limited to just this part of `createIterationCountCheck` then the IR should be well formed.

https://github.com/llvm/llvm-project/pull/153495