[llvm] Reapply [X86][ARM] Invert the low bit to get the inverse predicate (NFC) (PR #152053)

[Abhishek Kaushik via llvm-commits]

https://github.com/abhishek-kaushik22 commented:

Can you please document this so it doesn't break in the future as was requested in the previous PR?

> This happens to be true. It's completely undocumented that this is something that should be maintained for anyone coming to add new condition codes to the corresponding enum. At the very least you must document this.

https://github.com/llvm/llvm-project/pull/152053