[gtk+] quartz: Fix Makefile typo

[Benjamin Otte <otte src gnome org>]

commit 12d22dc8113023551173fff59d047210967a45e4
Author: Benjamin Otte <otte redhat com>
Date:   Wed May 15 01:52:32 2013 +0200

    quartz: Fix Makefile typo

 gdk/Makefile.am |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/gdk/Makefile.am b/gdk/Makefile.am
index af0ac94..379ea28 100644
--- a/gdk/Makefile.am
+++ b/gdk/Makefile.am
@@ -171,7 +171,7 @@ libgdk_3_la_LIBADD += x11/libgdk-x11.la
 endif # USE_X11
 
 if USE_QUARTZ
-libgdk_3_la_CFLAGS = -xobjective-c
+libgdk_3_la_CFLAGS += -xobjective-c
 libgdk_3_la_LIBADD += quartz/libgdk-quartz.la
 endif # USE_QUARTZ