Look into reorganizing pass pipeline

[Keno]

There's some feedback from upstream that our pass pipeline is suboptimal. Look into this
to see if there are any compile/runtime improvements to be had.

[maleadt]

Note from external codegen: it would be useful to have a PMbuiler-like extension mechanism, to inject eg. NVPTX-specific passes where appropriate, instead of after the fact. Might be appropriate to think about when reorganizing the passes.

[gbaraldi]

This has happened a couple of times and now we have moved to LLVMs NewPM