[jhbuild] Fix building gtk2 with quartz

[Ryan Lortie <desrt src gnome org>]

commit 16de750cfd65598f5c4ca1621949d256d13da6af
Author: Patrick Griffis <tingping tingping se>
Date:   Mon Jan 5 15:58:30 2015 -0500

    Fix building gtk2 with quartz

 modulesets/gnome-suites-core-deps-3.16.modules |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)
---
diff --git a/modulesets/gnome-suites-core-deps-3.16.modules b/modulesets/gnome-suites-core-deps-3.16.modules
index 4575a3f..8e0968b 100644
--- a/modulesets/gnome-suites-core-deps-3.16.modules
+++ b/modulesets/gnome-suites-core-deps-3.16.modules
@@ -1525,6 +1525,9 @@
 
   <autotools id="gtk+-2">
     <branch checkoutdir="gtk+-2" module="gtk+" revision="gtk-2-24"/>
+    <if condition-set="quartz">
+      <autogenargs value="--with-backend=quartz"/>
+    </if>
     <dependencies>
       <dep package="glib"/>
       <dep package="cairo"/>