Allow builds with glibc 2.20.
Based on a patch by Peter Hutterer <peter.hutterer@who-t.net>.
See <https://raw.githubusercontent.com/openembedded/oe-core/master/meta/recipes-graphics/xorg-driver/xf86-input-synaptics/always_include_xorg_server.h.patch>.

--- xf86-video-intel-2.21.15/src/intel_device.c.~1~	2013-08-09 16:58:48.000000000 -0400
+++ xf86-video-intel-2.21.15/src/intel_device.c	2014-12-18 00:03:54.700759577 -0500
@@ -33,6 +33,8 @@
 
 #include <sys/ioctl.h>
 
+#include <xorg-server.h>
+
 #include <pciaccess.h>
 #include <xf86.h>
 #include <xf86drm.h>