Fixes build with Python >= 3.6:

------
Making all in libgnomeui
make[2]: Entering directory '/tmp/guix-build-libgnomeui-2.24.5.drv-0/libgnomeui-2.24.5/libgnomeui'
  GEN    stamp-gnome-marshal.h
  GEN    stamp-gnometypebuiltins.h
INFO: Reading ./gnome-marshal.list...
  GEN    gnome-marshal.h
Traceback (most recent call last):
  File "/gnu/store/...-glib-2.54.2-bin/bin/glib-mkenums", line 688, in <module>
    process_file(fname)
  File "/gnu/store/...-glib-2.54.2-bin/bin/glib-mkenums", line 420, in process_file
    line = curfile.readline()
  File "/gnu/store/...-python-3.6.3/lib/python3.6/codecs.py", line 321, in decode
    (result, consumed) = self._buffer_decode(data, self.errors, final)
UnicodeDecodeError: 'utf-8' codec can't decode byte 0xf1 in position 1009: invalid continuation byte
make[2]: *** [Makefile:1109: stamp-gnometypebuiltins.h] Error 1
make[2]: Leaving directory '/tmp/guix-build-libgnomeui-2.24.5.drv-0/libgnomeui-2.24.5/libgnomeui'
make[1]: *** [Makefile:369: all-recursive] Error 1
make[1]: Leaving directory '/tmp/guix-build-libgnomeui-2.24.5.drv-0/libgnomeui-2.24.5'
make: *** [Makefile:296: all] Error 2
------

Patch copied from upstream source repository:

https://git.gnome.org/browse/libgnomeui/commit/?id=30334c28794ef85d8973f4ed0779b5ceed6594f2

From 30334c28794ef85d8973f4ed0779b5ceed6594f2 Mon Sep 17 00:00:00 2001
From: Colin Walters <walters@verbum.org>
Date: Mon, 7 Aug 2017 13:15:26 -0400
Subject: [PATCH] gnome-scores.h: Convert to UTF-8

The new Python `glib-mkenums` barfs on ISO-8859-1 input.
---
 libgnomeui/gnome-scores.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libgnomeui/gnome-scores.h b/libgnomeui/gnome-scores.h
index 911b12d1..4e641d22 100644
--- a/libgnomeui/gnome-scores.h
+++ b/libgnomeui/gnome-scores.h
@@ -27,7 +27,7 @@
  * "High Scores" Widget 
  *
  * AUTHOR: 
- * Horacio J. Peña <horape@compendium.com.ar>
+ * Horacio J. Peña <horape@compendium.com.ar>
  *
  * This is free software (under the terms of the GNU LGPL)
  *
rm>
</td></tr></table>
<div class='path'>path: <a href='/guix/log/?id=0f763db448758c8b7b9ae91d6870f75fc0ff987b'>root</a>/<a href='/guix/log/gnu?id=0f763db448758c8b7b9ae91d6870f75fc0ff987b'>gnu</a>/<a href='/guix/log/gnu/packages?id=0f763db448758c8b7b9ae91d6870f75fc0ff987b'>packages</a>/<a href='/guix/log/gnu/packages/axoloti.scm?id=0f763db448758c8b7b9ae91d6870f75fc0ff987b'>axoloti.scm</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/gnu/packages/axoloti.scm?id=0f763db448758c8b7b9ae91d6870f75fc0ff987b&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2017-12-16 09:01:57 +0100'>2017-12-16</span></td><td><a href='/guix/commit/gnu/packages/axoloti.scm?id=341bddb31542d03bef35b1234e6e9466be337798'>gnu: axoloti-runtime: Update ChibiOS URL.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/axoloti.scm (axoloti-runtime)[inputs]: Update URL for ChibiOS
sources.
</span></span></td><td>Ricardo Wurmus</td></tr>
<tr><td><span title='2017-10-17 17:32:20 +0200'>2017-10-17</span></td><td><a href='/guix/commit/gnu/packages/axoloti.scm?id=94b55ace14c09802298b5d2dc4e60dbad3ef6982'>gnu: axoloti-runtime: Update home page.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/axoloti.scm (axoloti-runtime)[home-page]: Use redirection
target URL.
</span></span></td><td>Ricardo Wurmus</td></tr>
<tr><td><span title='2017-10-17 16:49:20 +0200'>2017-10-17</span></td><td><a href='/guix/commit/gnu/packages/axoloti.scm?id=d991b0566433b0ff78dd92165430da2f40fe721d'>gnu: Add Axoloti.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/axoloti.scm: New file.
* gnu/packages/patches/libusb-for-axoloti.patch: New file.
* gnu/local.mk (dist_patch_DATA): Add patch.
(GNU_SYSTEM_MODULES): Add module.
</span></span></td><td>Ricardo Wurmus</td></tr>