This is still WIP, and unfortunately it doesn't work.  Here's the error
I got:

                 from ./drivers/pulseaudio/audio_driver_pulseaudio.h:36,
                 from platform/x11/os_x11.h:46,
                 from platform/x11/godot_x11.cpp:30:
  /gnu/store/iwgi9001dmmihrjg4rqhd6pa6788prjw-glibc-2.24/include/bits/local_lim.h:38:26: fatal error: linux/limits.h: No such file or directory
  #include <linux/limits.h>

I also get this if I try to build it outside the package, from a git
checkout of Godot.

I don't know why I'm experiencing this; I added linux-libre-headers as
an input.  It seems that I'm not the first one to experience this with
Guix packages... I ran across these:

  https://lists.gnu.org/archive/html/help-guix/2016-06/msg00130.html

(I don't think I need to include gcc-toolchain though)

  https://gnunet.org/bot/log/guix/2016-07-27
  https://gnunet.org/bot/log/guix/2016-08-03

looks like jlicht eventually found a solution, and lfam said
   <lfam> jlicht: Have you tried setting -I in #:make-flags or #:configure-flags?

... not sure how that helps with scons :)

Other potential issues:
 - bundles a number of packages (can they be easily unbundled?)
 - license field should probably reflect bundled packages
 - very badly snarfs a whole bunch of phases code from aria-maestosa,
   which itself suggests refactoring into a scons-build-system...

Nonetheless, uh, maybe it's a good starting point!