Restore InputMode For Module Interface

lib/Frontend/ModuleInterfaceLoader.cpp

@@ -1142,6 +1142,8 @@ void InterfaceSubContextDelegateImpl::inheritOptionsForBuildingInterface(
     genericSubInvocation.setSDKPath(SearchPathOpts.SDKPath);
   }
 
+  genericSubInvocation.getFrontendOptions().InputMode
+      = FrontendOptions::ParseInputMode::SwiftModuleInterface;
   if (!SearchPathOpts.RuntimeResourcePath.empty()) {
     genericSubInvocation.setRuntimeResourcePath(SearchPathOpts.RuntimeResourcePath);
   }