[llvm] [SCEV] Use context sensative reasoning in howFarToZero (PR #94525)

[Philip Reames via llvm-commits]

preames wrote:

> It would be better to use applyLoopGuards, which should be cheaper and also provide better results for the queries you are performing here.

How would loop guards help prove the 

https://github.com/llvm/llvm-project/pull/94525