Building gtkmm 3 under win32 (mingw)

[Netrick <netrick o2 pl>]

Hi, 
gtkmm is the best C++ gui lib. However, it claims to be crossplatform but last gtkmm (and gtk+) windows binaries are for old 2.2x versions. How can I compile it on windows using mingw 4.7? It seems like I also need to compile gtk 3.4 on windows but it also isn't straightforward. So, is gtkmm 3.x really crossplatform? Any good ways to compile gtkmm (including gtk+) on mingw? Or maybe pre built binaries?
 
Thanks