[llvm] improve debug messages in delinearization and dependence analysis (NFC) (PR #156339)

[Ryotaro Kasuga via llvm-commits]

https://github.com/kasuga-fj commented:

Please update the title and description.

- This is not NFC. I don't think changing debug messages qualifies as NFC. Additionally, in this case, the test results have changed.
- This PR doesn't modify DA.

I'll approve once all my comments have been *addressed*. Note that I'm not asking you to make every change exactly as suggested. If you have some reason, it's totally fine to leave things as they are.

https://github.com/llvm/llvm-project/pull/156339