synergy: fix dependencies

Synergy can be used without a local X server, and Xinerama is an optional
dependency.

Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

package/synergy/synergy.mk

@@ -10,6 +10,7 @@ SYNERGY_SITE = http://$(BR2_SOURCEFORGE_MIRROR).dl.sourceforge.net/sourceforge/s
 SYNERGY_CONF_OPT = --x-includes=$(STAGING_DIR)/usr/include/X11 \
                    --x-libraries=$(STAGING_DIR)/usr/lib
 
-SYNERGY_DEPENDENCIES = xserver_xorg-server xlib_libXtst
+SYNERGY_DEPENDENCIES = xlib_libXtst \
+		$(if $(BR2_PACKAGE_XLIB_LIBXINERAMA),xlib_libXinerama)
 
 $(eval $(call AUTOTARGETS))