[llvm] [TailRecElim] Handle discarded-call return conflicts with a shift accumulator (PR #221694)

[Federico Bruzzone via llvm-commits]

FedericoBruzzone wrote:

> Looks reasonable, thanks!
> 
> (Per the [DeveloperPolicy](https://llvm.org/docs/DeveloperPolicy.html#commit-messages), we usually prefer not to tag people in PR description / commit message, so as to avoid receiving spurious notifications on cherry-picks.)

Thank you for your review, as always @antoniofrighetto :D

You're right, I removed the tag. I recently came across [this discussion on Discourse](https://discourse.llvm.org/t/forbidding-username-in-commits/86997/17) and thought GitHub would remove the notification for the PR description as well, but I was wrong :'D

https://github.com/llvm/llvm-project/pull/221694