[llvm] [llvm-exegesis] [AArch64] Add support for Load Instructions in subprocess execution mode (PR #144895)

[Aiden Grossman via llvm-commits]

https://github.com/boomanaiden154 requested changes to this pull request.

> Unreliable measurements due to ioctl syscall failing, file descriptor for perf event is not populated at auxiliary memory location where it is expected. (Inclined to take up this in future)
(FYI) All Memory mapping is anonymous, not a functional problem. (Inclined to take up this in future)

Both of these need to be fixed before this PR can land. It doesn't make sense to support subprocess execution mode in exegesis when getting a cycles count does not work at all. Keeping all memory mappings anonymous also breaks the semantics of how the memory is supposed to be managed.

https://github.com/llvm/llvm-project/pull/144895