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

[Stefan Gränitz via llvm-commits]

weliveindetail wrote:

> 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
> ```

Yeah, sounds great! It would allow to run multiple instances with different scripts. Right now, we cannot really associate command-line options with plugin instances. However, I think we should get the status quo testable first. Thanks for your review @serge-sans-paille! 


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