[llvm] [CodeGen][Pass] Add `TargetPassBuilder` (PR #137290)

[via llvm-commits]

paperchalice wrote:

> But there are no virtual methods, so are we removing distinct phases (like `addPreEmitPasses()`) completely and only using `injectBefore()` now?

IMHO some phases here is not clear, the example is pre emit, we have `addPreEmitPasses` and `addPreEmitPasses2()` thus here only provides `injectBefore`.

> If we don't want overrides (virtual/CRTP) we could add "phase marker" passes (that are dummy passes like `ISelPrepareBegin()`) to be used with `injectBefore`.

Yeah pre isel is one of phases `injectBefore()` can't handle easily, may add them in future.



https://github.com/llvm/llvm-project/pull/137290