[llvm] [LoopInterchange] Add tests of 'S' deps (NFC) (PR #125214)

[Ryotaro Kasuga via llvm-commits]

kasuga-fj wrote:

IIUIC, existing 'S' deps tests are the cases where we cannot interchange for now, but they are in principle legal to exchange. The original purpose of tests marked as XFAIL is to make sure that the interchange happens as we expect. On the other hand, tests in this patch are cases where interchanging is not allowed because it changes the original semantics, but it was done before #119345 due to the mishandling of 'S' deps. So these are tests to make sure that illegal interchange doesn't happen forever in the future. In other words, these tests can prevent bugs fixed in #119345 from recurring.

https://github.com/llvm/llvm-project/pull/125214