[llvm] [NewPM][CodeGen] add TargetPassConfig like API (PR #70906)

[Arthur Eubanks via llvm-commits]

================
@@ -1105,7 +1305,8 @@ void CodeGenPassBuilder<Derived>::addOptimizedRegAlloc(
   // PreRA instruction scheduling.
   addPass(MachineSchedulerPass());
 
-  if (derived().addRegAssignmentOptimized(addPass)) {
+  Error Err = derived().addRegAssignAndRewriteOptimized(addPass);
----------------
aeubanks wrote:

why introduce a variable?

https://github.com/llvm/llvm-project/pull/70906