[llvm] [AArch64] Add predicate-as-counter loop rewrite pass (PR #220960)

[Benjamin Maxwell via llvm-commits]

MacDue wrote:

Moving the passes around results in ~no regression: https://llvm-compile-time-tracker.com/compare.php?from=9e0686cca51613229ef85788ee5d1deee0595b92&to=09fafae96ee5ab7f5e07e8010fad0e7be15ca7be&stat=instructions%3Au (but also no speedup on the CTT). So we could make the passes optional, but it's probably not necessary yet. 

https://github.com/llvm/llvm-project/pull/220960