[llvm] [LLVM] treat `@llvm.ssub.sat` the same as `@llvm.aarch64.neon.sqsub` (PR #140454)

[Folkert de Vries via llvm-commits]

folkertdev wrote:

hmm, apparently I messed up some flags. On CI, and with the command from the top of the file, it looks like some `mov`s get inserted in an unexpected place. I have no idea why that would be the case. 

Also a bunch of the `; CHECK-GI-NEXT:  warning:` lines added in the first command have disappeared when I run the tests now?!

https://github.com/llvm/llvm-project/pull/140454