mingw-gtk2: BuildRequire packages needed for regenerating configure
    
    gtk2 has switched to using AM_MAINTAINER_MODE([enable]), which means
    that changes to configure.in will result in the configure script getting
    regenerated.
    
    gtk-fix-out-of-source-build.patch (can we get this upstream or drop it,
    please?) patches configure.in, so we need to BR the packages.