[clang] [llvm] [AArch64][SelectionDAG] Add CodeGen support for scalar FEAT_CPA (PR #105669)

[Alexander Richardson via cfe-commits]

arichardson wrote:

> > If you would like to credit the original author for the PTRADD nodd that would be @davidchisnall (and probably some parts by @jrtc27, although that might just be the combines). I don't see any problems in landing that part separately
> 
> Sounds like a good use for GitHub's [co-authors](https://github.blog/news-insights/product-news/commit-together-with-co-authors/) feature (as suggested by the [LLVM dev policy](https://llvm.org/docs/DeveloperPolicy.html#commit-messages)). So, @davidchisnall as `--author`, with @jrtc27 and @rgwott as `Co-authored-by`, and also you, @arichardson, since you contributed the infinite combine fix?

@ritter-x2a thanks for picking this up, that sounds perfect.

https://github.com/llvm/llvm-project/pull/105669