[llvm] [NewPM][CodeGen] Refactoring CodeGenPassBuilder (PR #89708)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> > can you expand on the commit description? e.g. I'm not sure what "Support pass substitution" means.
> 
> Some targets (ARM, RISCV etc.) and option `--misched-postra` require use `PostMachineSchedulerPass` rather `PostRASchedulerPass`, in fact, this is the only use of this function.
> 

We should finally finish that migration...


https://github.com/llvm/llvm-project/pull/89708