[llvm] [RegAlloc][AArch64] Add test case for terminal rule. NFC (PR #170035)

[David Green via llvm-commits]

https://github.com/davemgreen commented:

Can we just update_mir_test_checks the test?

I believe we saw a number of perf regressions after #168661 from loops that contained extra copies that were not present before. IIUC the performance went back down in some cases to where they were before the terminal rule was enabled.

https://github.com/llvm/llvm-project/pull/170035