[objc] [fcp] only emit property_control tag when we have non-None property_control

Summary: Plugin can emit corrupt data when ObjCPropertyDecl == None

Reviewed By: ezgicicek, jvillard

Differential Revision: D25023778

fbshipit-source-id: 30b950f7a

facebook-clang-plugins/libtooling/ASTExporter.h

@@ -2859,8 +2859,8 @@ void ASTExporter<ATDWriter>::VisitObjCPropertyDecl(const ObjCPropertyDecl *D) {
     case ObjCPropertyDecl::Optional:
       OF.emitSimpleVariant("Optional");
       break;
-    case ObjCPropertyDecl::None:
+    default:
-      llvm_unreachable("unreachable");
+      OF.emitSimpleVariant("None");
       break;
     }
   }