[llvm] [clang] [CodeGen] Port AtomicExpand to new Pass Manager (PR #71220)

[Matt Arsenault via cfe-commits]

================
@@ -457,7 +457,7 @@ TargetPassConfig *PPCTargetMachine::createPassConfig(PassManagerBase &PM) {
 void PPCPassConfig::addIRPasses() {
   if (TM->getOptLevel() != CodeGenOptLevel::None)
     addPass(createPPCBoolRetToIntPass());
-  addPass(createAtomicExpandPass());
+  addPass(createAtomicExpandLegacyPass());
----------------
arsenm wrote:

We should probably just add this to the default pipeline (not in this change) 

https://github.com/llvm/llvm-project/pull/71220