[llvm] [NewPM][BPF] Add `BPFCodeGenPassBuilder` (PR #94158)

[Arthur Eubanks via llvm-commits]

aeubanks wrote:

> > > Code churn and nothing more. No.
> > 
> > 
> > can you clarify your comment? we're trying to make codegen work with the new pass manager
> 
> all TODO are screaming that this is useless change. Why do you want empty callbacks with TODO comments?

because we're going to implement them in a followup change

this PR is just boilerplate and doesn't actually do much. however, it makes follow-up changes smaller which is valuable for reviewing

https://github.com/llvm/llvm-project/pull/94158