[llvm] [Exegesis][AArch64] Use more generic cycles counter (PR #133376)

[David Green via llvm-commits]

https://github.com/davemgreen approved this pull request.

I've ran into this before but never bottomed out what the difference between the two was. I tested on a couple of machines and it did OK on both (one of which worked before, one of which didn't).

LGTM, thanks.

https://github.com/llvm/llvm-project/pull/133376