[llvm] [Pipeliner] Fix Phi node dependency calculation (PR #160056)

[Yuta Mukai via llvm-commits]

ytmukai wrote:

`mayOverlapInLaterIter()` should only return false when it is guaranteed that there are no dependencies. Otherwise, it may lead to incorrect scheduling. This change seems to allow the function to return false even when dependencies could exist.

https://github.com/llvm/llvm-project/pull/160056