[clang] Don't make synthesized accessor stub functions visible twice

[teemperor]

Summary

addDecl is making the Decl visible, so there is no need to make it explicitly
visible again. Making it visible twice will also make the lookup storage less
efficient and potentially lead to crashes, see D84827 for that.

[aprantl]

All for deleting the cargo-cult code. Thanks!

clang/lib/Sema/SemaDeclObjC.cpp

Decl *Sema::ActOnAtEnd(Scope *S, SourceRange AtEnd, ArrayRef<Decl *> allMethods,
 
   // Make synthesized accessor stub functions visible.
   // ActOnPropertyImplDecl() creates them as not visible in case
   // they are overridden by an explicit method that is encountered
   // later.
   if (auto *OID = dyn_cast<ObjCImplementationDecl>(CurContext)) {
     for (auto PropImpl : OID->property_impls()) {
       if (auto *Getter = PropImpl->getGetterMethodDecl())
-        if (Getter->isSynthesizedAccessorStub()) {
-          OID->makeDeclVisibleInContext(Getter);
+        if (Getter->isSynthesizedAccessorStub())
           OID->addDecl(Getter);
-        }
       if (auto *Setter = PropImpl->getSetterMethodDecl())
-        if (Setter->isSynthesizedAccessorStub()) {
-          OID->makeDeclVisibleInContext(Setter);
+        if (Setter->isSynthesizedAccessorStub())
           OID->addDecl(Setter);
-        }
-    }
-  }
 
   // FIXME: Remove these and use the ObjCContainerDecl/DeclContext.
   llvm::DenseMap<Selector, const ObjCMethodDecl*> InsMap;
   llvm::DenseMap<Selector, const ObjCMethodDecl*> ClsMap;
 
   for (unsigned i = 0, e = allMethods.size(); i != e; i++ ) {
     ObjCMethodDecl *Method =
       cast_or_null<ObjCMethodDecl>(allMethods[i]);