[llvm] [LoopInterchange] Increment isDirectionNegative check to next level for scalar direction (PR #78951)

[Michael Kruse via llvm-commits]

Meinersbur wrote:

I would need a more convincing argument than "it makes my case work".

Suppose the scalar dependency is an implicit `<` dependencies. 
```
for (int i = 0; i < n; ++i)
  a=a/i;
```
This example would not be reversed because there is no inner level but consider this to be the "either way goes" case.
Reversing the scalar dependence would make a `>`-dependence out of it, which is definitely wrong because it would make it depend on the future (which `normalize()` is supposed to normalize).

Possibly, `normalize()` would also need to reverse the direction of scalar dependencies, but I would need some more thoughts on why 

https://github.com/llvm/llvm-project/pull/78951