MLIR] Fix documentation of the `ExecutionEngine` in the toy tutorial example

mlir/docs/Tutorials/Toy/Ch-6.md

int runJit(mlir::ModuleOp module) {
 
   // An optimization pipeline to use within the execution engine.
   auto optPipeline = mlir::makeOptimizingTransformer(
       /*optLevel=*/EnableOpt ? 3 : 0, /*sizeLevel=*/0,
       /*targetMachine=*/nullptr);
 
   // Create an MLIR execution engine. The execution engine eagerly JIT-compiles
   // the module.
-  auto maybeEngine = mlir::ExecutionEngine::create(module, optPipeline);
+  auto maybeEngine = mlir::ExecutionEngine::create(module,
+      /*llvmModuleBuilder=*/nullptr, optPipeline);
   assert(maybeEngine && "failed to construct an execution engine");
   auto &engine = maybeEngine.get();
 
   // Invoke the JIT-compiled function.
   auto invocationResult = engine->invoke("main");
   if (invocationResult) {
     llvm::errs() << "JIT invocation failed\n";
     return -1;