[ArgPromo] Preserve FunctionAnalysisManagerCGSCCProxy

[aeubanks]

Summary

We already make sure to properly clear analyses for deleted functions.

This makes investigating some future potential compile time improvements easier.

llvm/lib/Transforms/IPO/ArgumentPromotion.cpp

do {
     }
 
     Changed |= LocalChange;
   } while (LocalChange);
 
   if (!Changed)
     return PreservedAnalyses::all();
 
-  return PreservedAnalyses::none();
+  PreservedAnalyses PA;
+  // We've cleared out analyses for deleted functions.
+  PA.preserve<FunctionAnalysisManagerCGSCCProxy>();
+  return PA;
 }
 
 namespace {
 
 /// ArgPromotion - The 'by reference' to 'by value' argument promotion pass.
 struct ArgPromotion : public CallGraphSCCPass {
   // Pass identification, replacement for typeid
   static char ID;