[llvm] [llvm-exegesis][AArch64] Check for PAC keys before disabling them (PR #138643)

[Tulio Magno Quites Machado Filho via llvm-commits]

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

@abhilash1910 Given the following comment from @atrosinenko:

> it is probably safer to only execute tests with the --aarch64-keep-pac-keys option (for usability, it may be better to define an inverted option instead, so that key control logic is disabled unless explicitly requested)

I expected to see changes in this PR in order to guarantee that tests wouldn't start to fail.
Did I miss anything?

https://github.com/llvm/llvm-project/pull/138643