triggerhappy: add optional dependency on systemd

triggerhappy can use systemd for socket activation.

Cc: Peter Korsgaard <peter@korsgaard.com>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/triggerhappy/triggerhappy.mk

@@ -10,6 +10,10 @@ TRIGGERHAPPY_LICENSE = GPL-3.0+
 TRIGGERHAPPY_LICENSE_FILES = COPYING
 TRIGGERHAPPY_DEPENDENCIES = host-pkgconf
 
+ifeq ($(BR2_PACKAGE_SYSTEMD),y)
+TRIGGERHAPPY_DEPENDENCIES += systemd
+endif
+
 define TRIGGERHAPPY_BUILD_CMDS
 	$(MAKE) $(TARGET_CONFIGURE_OPTS) PKGCONFIG="$(PKG_CONFIG_HOST_BINARY)" \
 		-C $(@D) thd th-cmd