[llvm] [AArch64] improve zero-cycle regmov test (PR #143680)

[Tomer Shafir via llvm-commits]

tomershafir wrote:

v2:
- Removed `nownwind` and `ssp` from `t` function decleration
- Removed `nounwind` from `foo` call sites

https://github.com/llvm/llvm-project/pull/143680