[llvm] [LoopInterchange] Constrain LI within supported loop nest depth (PR #118656)

[Sjoerd Meijer via llvm-commits]

sjoerdmeijer wrote:

Looks good to me too, but I would really prefer not to introduce tests that rely on Debug when not needed.

The way I look at: with ```deep-loop-nest.ll``` we test the loop depth. With the default value of 10, it shouldn't trigger, but we may want another RUN line with ```-loop-interchange-max-loop-nest-depth=11``` where it does trigger, so we have a negative and positive test, and we can fully rely on optimisation remarks for that, no need for Debug. 

Testing when DependencyAnalysis is or isn't running, is slightly orthogonal? Can this be tested separated with a different test that then depends on Debug?

But anyway, this is my preference, am also not blocking this. 



https://github.com/llvm/llvm-project/pull/118656