Hello! Since images tell thousand words, here are few that show latest gtkmm 3 in currently most recent Visual Studio:
Hint: click on image to enlarge.
Please note that this site is just a shortcut to let you direct to right place, for full details and step by step tutorial refer to wiki (link below) which will lead you ahead.
If you stuck compiling at some point feel free to ask for help in comment section bellow or by opening an issue on GitHub.
I made a wiki on GitHub where you can learn about details on how to compile everything from source in Visual Studio, also on the same page you will find Visual Studio projects and other requirements.