x11r7/xserver_xorg-server: --enable-glamor & libepoxy: glamor build dependency

	* enable Glamor support (which handles DRI3) for the
	  modesetting driver.

	  http://www.freedesktop.org/wiki/Software/Glamor/

Signed-off-by: Xerxes Rånby <xerxes@gudinna.com>