[llvm] Changed stat passes to count instructions before and after optimizations (PR #188837)

[Arthur Eubanks via llvm-commits]

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

we actually use the STATISTIC name in the output right? I'd fully spell out "Opt" -> "Optimization", e.g. `Num##Name##PreOptimization`

otherwise lgtm, thanks!

https://github.com/llvm/llvm-project/pull/188837