package/sslh: add optional systemd dependency

systemd dependency has been added in version 1.18 with
https://github.com/yrutschle/sslh/commit/b3f48d98767634007dbe29ee3cb609a2e4283b7d

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

package/sslh/sslh.mk

@@ -27,6 +27,13 @@ else
 SSLH_MAKE_OPTS += USELIBPCRE=
 endif
 
+ifeq ($(BR2_PACKAGE_SYSTEMD),y)
+SSLH_DEPENDENCIES += systemd
+SSLH_MAKE_OPTS += USESYSTEMD=1
+else
+SSLH_MAKE_OPTS += USESYSTEMD=
+endif
+
 define SSLH_BUILD_CMDS
 	$(TARGET_MAKE_ENV) $(MAKE) $(SSLH_MAKE_OPTS) -C $(@D)
 endef