[llvm] [llvm-exegesis] Implement the loop repetition mode for AArch64 (PR #154751)

[Sjoerd Meijer via llvm-commits]

sjoerdmeijer wrote:

Thanks for the review @boomanaiden154 ! I will fix that before merging this.

One semi-related question to this: do you know if you `--min-instructions` is supposed to work with `-repetition-mode=loop`? I would like to increase the loop body, but `--min-instructions` only seem to have an effect when in duplicate mode. Option `middle-half-loop` seem to achieve what I want, it gives me more accurate numbers for the couple of examples I've tried, but was wondering if I could control this sort of behaviour myself with min-instructions.

https://github.com/llvm/llvm-project/pull/154751