Use gdb for debug dialog on Win32 too
After discussing on IRC, we discussed it may be worth just use gdb on Windows. @jernejs already confirmed that is no problem to just ship win-gdb there.
This would most likely mean we would drop the DrMingw support (unless we keep both, but really stack trace quality is so different that I wonder if that is worth keeping DrMingw). Also using a debugger allows us to attach anytime to the GIMP process, hence debugging also warning/criticals (not only crashes).
I open this report as a reminder for myself (though anyone is welcome to update the code first, just set yourself as assignee once you start working so we don't work on the same thing).