[llvm] Add support for single reductions in ComplexDeinterleavingPass (PR #112875)

[Nicholas Guy via llvm-commits]

NickGuy-Arm wrote:

> Reverted for now in [76714be](https://github.com/llvm/llvm-project/commit/76714be5fd4ace66dd9e19ce706c2e2149dd5716) as this has been breaking most stage2 builds on AArch64 for 4+ hours

Thanks, I'm now testing a fix with a local stage2 build. Not sure why I didn't receive the buildbot emails though, so I didn't realise it was failing things at first.

https://github.com/llvm/llvm-project/pull/112875