How to replicate C code instantiating a GTK_WIDGET

[PMunch]

Remember that you also need to get your include paths set up correctly. If it's 
any help 
[here](https://github.com/PMunch/futhark/issues/63#issuecomment-1474256338) is 
an older snippet of my Gtk binding with Futhark. The last line there is the 
equivalent of `GTK_WIDGET`.