xserver_xorg-server: Add optional package xlib_libXcomposite as dependency

Make sure that xlib_libXcomposite is build before xserver_xorg-server.

With this defconfig

BR2_TOOLCHAIN_EXTERNAL=y
BR2_PACKAGE_XORG7=y
BR2_PACKAGE_XSERVER_XORG_SERVER=y
BR2_PACKAGE_XSERVER_XORG_SERVER_MODULAR=y
BR2_PACKAGE_XLIB_LIBXCOMPOSITE=y

and "make xserver_xorg-server" the package xlib_libXcomposite was ignored.

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/x11r7/xserver_xorg-server/xserver_xorg-server.mk

@@ -161,7 +161,9 @@ ifneq ($(BR2_PACKAGE_XLIB_LIBXVMC),y)
 XSERVER_XORG_SERVER_CONF_OPTS += --disable-xvmc
 endif
 
-ifneq ($(BR2_PACKAGE_XLIB_LIBXCOMPOSITE),y)
+ifeq ($(BR2_PACKAGE_XLIB_LIBXCOMPOSITE),y)
+XSERVER_XORG_SERVER_DEPENDENCIES += xlib_libXcomposite
+else
 XSERVER_XORG_SERVER_CONF_OPTS += --disable-composite
 endif