Fixing `FileNotFoundError: [Errno 2] No such file or directory: 'llvm-config'`

I’ve created a starter patch here: Starter patch · stuartarchibald/llvmlite@e7dd319 · GitHub there’s a doc in the root of the llvmlite repo with some notes and a small patch to build.py to hide the issue relating to LLVM to encourage users to read the per-prepared advice.