gnu: libgnome: Adjust for latest GLib.

* gnu/packages/patches/libgnome-encoding.patch: New file.
* gnu/packages/gnome.scm (libgnome)[source]: Use it.
* gnu/local.mk (dist_patch_DATA): Add it.

gnu/local.mk

@@ -813,6 +813,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/libgit2-0.25.1-mtime-0.patch		\
   %D%/packages/patches/libgdata-fix-tests.patch			\
   %D%/packages/patches/libgdata-glib-duplicate-tests.patch	\
+  %D%/packages/patches/libgnome-encoding.patch			\
   %D%/packages/patches/libgxps-CVE-2017-11590.patch		\
   %D%/packages/patches/libffi-3.2.1-complex-alpha.patch		\
   %D%/packages/patches/libjxr-fix-function-signature.patch	\

gnu/packages/gnome.scm

@@ -1,6 +1,6 @@
 ;;; GNU Guix --- Functional package management for GNU
 ;;; Copyright © 2013, 2015 Andreas Enge <andreas@enge.fr>
-;;; Copyright © 2014, 2015, 2016, 2017 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2014, 2015, 2016, 2017, 2018 Ludovic Courtès <ludo@gnu.org>
 ;;; Copyright © 2014 Ian Denhardt <ian@zenhack.net>
 ;;; Copyright © 2014, 2016 Eric Bavier <bavier@member.fsf.org>
 ;;; Copyright © 2014, 2015 Federico Beffa <beffa@fbengineering.ch>
@@ -1484,7 +1484,8 @@ to access local and remote files with a single consistent API.")
                                   name "-" version ".tar.bz2"))
               (sha256
                (base32
-                "197pnq8y0knqjhm2fg4j6hbqqm3qfzfnd0irhwxpk1b4hqb3kimj"))))
+                "197pnq8y0knqjhm2fg4j6hbqqm3qfzfnd0irhwxpk1b4hqb3kimj"))
+              (patches (search-patches "libgnome-encoding.patch"))))
     (build-system gnu-build-system)
     (arguments
      `(#:phases

gnu/packages/patches/libgnome-encoding.patch

@@ -0,0 +1,16 @@
+Remove non-UTF-8 character (this is a NO-BREAK SPACE character, encoded in
+ISO-8859-1) to fix build failure with 'glib-mkenums' in GLib 2.54.2+.
+
+Patch from <https://github.com/macports/macports-ports/commit/1f3efc8e65cc060d1701407bd1e56e62e6bd9c55>.
+
+--- a/libgnome/gnome-config.h	2009-04-23 04:29:13.000000000 -0500
++++ b/libgnome/gnome-config.h	2017-10-04 02:17:22.000000000 -0500
+@@ -270,7 +270,7 @@ void gnome_config_clean_key_ (const char
+ #define gnome_config_private_clean_key(path) \
+ 	(gnome_config_clean_key_((path),TRUE))
+ 
+-/* returns the true filename of the config file */
++/* returns the true filename of the config file */
+ #define gnome_config_get_real_path(path) \
+ 	(g_build_filename (gnome_user_dir_get(),(path),NULL))
+ #define gnome_config_private_get_real_path(path) \