Looks good !!

The Gtk+ binaries I currently have won't allow me to build the latest version of Glib (1.321).
I take it that there's no such problem with the binaries you used ?
(If so I'll start using them instead of the ones I currently use.)

Update:

At the time of this writing (july 2016), the package installed using msys2 crashed on the tests with cairo

It might simply be that the msys2 package functions correctly in the msys2 environment, but is incompatible with the native Win32 environment of Strawberry Perl.
(You might find the msys2 package to be quite satisfactory if you build the Gtk+ modules with msys2's perl.)

Cheers,
Rob