[llvm] s390x: pattern match saturated truncation (PR #155377)

[Folkert de Vries via llvm-commits]

folkertdev wrote:

I added the 128-bit integer comparisons and support for PCKLS, and moved the multiclasses. Probably some naming/formatting nits remain, but otherwise it's looking alright.

https://github.com/llvm/llvm-project/pull/155377