optionally enable `Polly` passes in llvmlite

[dlee992]

I saw llvmlite is built with Polly:

llvmlite/conda-recipes/llvmdev_manylinux2014/build.sh

Line 28 in f59140f

_cmake_config+=(-DLINK_POLLY_INTO_TOOLS:BOOL=ON)

But the PassBuilder (or PassManager) in source code doesn't provide a way to optionally add Polly passes. Thus this is a feature request.

[stuartarchibald]

Thanks for the request. I recall attempting this at some time in the past and it was quite involved. I think once LLVM 18 is in use by llvmlite there's an API that will help with this (and loading in and using other passes too). It may however already be possible via some other means that has appeared since I last tried.