You can invoke devenv.exe /diff list1.txt list2.txt from the Visual Studio Developer Command Prompt or, if a Visual Studio instance is already running, you can type Tools.DiffFiles in the Command window, with a handy file name completion:
You can invoke devenv.exe /diff list1.txt list2.txt from the Visual Studio Developer Command Prompt or, if a Visual Studio instance is already running, you can type Tools.DiffFiles in the Command window, with a handy file name completion: