[clang] [lld] [llvm] [RFC] Initial reference pass-plugin in LLVM (PR #171111)

[via llvm-commits]

https://github.com/serge-sans-paille commented:

First round of review, just on the loader.

I also feel like we should be able to specify the name of the Python pass as pass plugin, instead of passing a generic pass with an extra opt, something like

```
clang -fpass-plugin=my/python/plugin.py
``` 

https://github.com/llvm/llvm-project/pull/171111