package/lxc: add systemd optional dependency

Fix the following build failure raised since bump to version 5.0.1 in
commit db19998035701d08bf1b5fd366e0b5aa9adb8e57:

Run-time dependency systemd found: NO (tried pkgconfig and cmake)

../output-1/build/lxc-5.0.1/config/init/systemd/meson.build:11:4: ERROR: Dependency "systemd" not found, tried pkgconfig and cmake

Fixes:
 - http://autobuild.buildroot.org/results/495175c367084093bc01c40290736c738d876894

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/lxc/lxc.mk

@@ -63,4 +63,19 @@ else
 LXC_CONF_OPTS += -Dopenssl=false
 endif
 
+ifeq ($(BR2_PACKAGE_SYSTEMD),y)
+LXC_CONF_OPTS += -Dsd-bus=enabled
+LXC_DEPENDENCIES += systemd
+else
+LXC_CONF_OPTS += -Dsd-bus=disabled
+endif
+
+ifeq ($(BR2_INIT_SYSTEMD),y)
+LXC_CONF_OPTS += -Dinit-script=systemd
+else ifeq ($(BR2_INIT_SYSV),y)
+LXC_CONF_OPTS += -Dinit-script=sysvinit
+else
+LXC_CONF_OPTS += -Dinit-script=
+endif
+
 $(eval $(meson-package))