[llvm] [SCEV] Add commutative add matchers (NFC) (PR #178663)

[Sayan Sivakumaran via llvm-commits]

sivakusayan wrote:

My usecase is that I want to match load SCEVs that look like `{{%ptr + offset}, +, step}` or `{{offset + %ptr}, +, step}` and extract the `offset` from them. Please let me know if I'm missing something and there is already a way to do this.

Also, it seems like the above build step is failing for other PRs too, here is [one example.](https://github.com/llvm/llvm-project/pull/178661#issuecomment-3818054059) I would open an issue myself but I don't think I have permission to add tags.

https://github.com/llvm/llvm-project/pull/178663