[llvm] [Utils] Consolidate `LockstepReverseIterator` into own header (NFC) (PR #116657)

[Antonio Frighetto via llvm-commits]

antoniofrighetto wrote:

> I think your reapplied attempt still has a build failure: https://lab.llvm.org/buildbot/#/builders/38/builds/2451/steps/8/logs/stdio at line 2741 https://lab.llvm.org/buildbot/#/builders/161/builds/4812 at line 99
> 
> I would have written this comment at the PR of the reapply commit - but it didn't have a PR -.-
> 
> One benefit of a PR is to have pre-merge bots checking if the code compiles, avoiding similar mistakes.

Fixed in 93b263a01cf898e609d3896edd0ce95789491bcd. The pre-merge checks had been already carried out within this PR, and so has been done locally running expensive checks for the reapply commit. The issue would have not been caught either with a new PR, just as it happened when David merged this the first time (despite bots being green).

https://github.com/llvm/llvm-project/pull/116657