[PATCH] Fix gtk-doc build

[Andy Wingo]

On media-updates, I had a failure building gtk-doc.  Not sure what is
causing this failure; was it always failing recently?  Strange stuff.

>From 8c9f2582199ad1321f564ed10937457facc9453c Mon Sep 17 00:00:00 2001
From: Andy Wingo <address@hidden>
Date: Wed, 24 Feb 2016 15:31:15 +0100
Subject: [PATCH] gnu: gtk-doc: Fix build.

* gnu/packages/gtk.scm (gtk-doc): Fix build.
---
 gnu/packages/gtk.scm | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/gnu/packages/gtk.scm b/gnu/packages/gtk.scm
index a234b89..9f2e514 100644
--- a/gnu/packages/gtk.scm
+++ b/gnu/packages/gtk.scm
@@ -1107,7 +1107,24 @@ information.")
                 "12xmmcnq4138dlbhmqa45wqza8dky4lf856sp80h6xjwl2g7a85l"))))
     (build-system gnu-build-system)
     (arguments
-     `(#:configure-flags
+     `(#:phases
+       (modify-phases %standard-phases
+         (add-before
+             'configure 'fix-docbook
+           (lambda* (#:key inputs #:allow-other-keys)
+             (substitute* "configure"
+               ;; The configure check is overzealous about making sure that
+               ;; things are in place -- it uses the xmlcatalog tool to make
+               ;; sure that docbook-xsl is available, but this tool can only
+               ;; look in one catalog file, unlike the $XML_CATALOG_FILES
+               ;; variable that Guix defines.  Fool the test by using the
+               ;; docbook-xsl catalog explicitly and get on with life.
+               (("\"\\$XML_CATALOG_FILE\" \
+\"http://docbook.sourceforge.net/release/xsl/";)
+                (string-append (assoc-ref %build-inputs "docbook-xsl")
+                               "/xml/xsl/docbook-xsl-1.78.1/catalog.xml \
+\"http://docbook.sourceforge.net/release/xsl/";))))))
+       #:configure-flags
        (list (string-append "--with-xml-catalog="
                             (assoc-ref %build-inputs "docbook-xml")
                             "/xml/dtd/docbook/catalog.xml"))))
-- 
2.6.3