package/rdesktop: add xlib_libXrandr optional dependency

xlib_libXrandr is an optional dependency since version 1.7.0 and
https://github.com/rdesktop/rdesktop/commit/6ee9faeffcd9dd2e4c262d732e15a3a02278578d

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/rdesktop/rdesktop.mk

@@ -9,7 +9,8 @@ RDESKTOP_SITE = $(call github,rdesktop,rdesktop,v$(RDESKTOP_VERSION))
 RDESKTOP_DEPENDENCIES = host-pkgconf openssl xlib_libX11 xlib_libXt \
 	$(if $(BR2_PACKAGE_ALSA_LIB_PCM),alsa-lib) \
 	$(if $(BR2_PACKAGE_LIBAO),libao) \
-	$(if $(BR2_PACKAGE_LIBSAMPLERATE),libsamplerate)
+	$(if $(BR2_PACKAGE_LIBSAMPLERATE),libsamplerate) \
+	$(if $(BR2_PACKAGE_XLIB_LIBXRANDR),xlib_libXrandr)
 RDESKTOP_CONF_OPTS = --with-openssl=$(STAGING_DIR)/usr --disable-credssp
 RDESKTOP_LICENSE = GPL-3.0+
 RDESKTOP_LICENSE_FILES = COPYING