package/tzdata: install leap-seconds.list into results

add leap-seconds.list to installed files so it can be used by other packages

specifically, ntpd's ntp.conf can now include:
leapfile /usr/share/zoneinfo/leap-seconds.list

Signed-off-by: David Johnson <dave-git@centerclick.org>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/tzdata/tzdata.mk

@@ -59,7 +59,7 @@ endef
 
 define HOST_TZDATA_INSTALL_CMDS
 	$(INSTALL) -d -m 0755 $(HOST_DIR)/share/zoneinfo
-	cp -a $(@D)/_output/* $(@D)/*.tab $(HOST_DIR)/share/zoneinfo
+	cp -a $(@D)/_output/* $(@D)/*.tab $(@D)/leap-seconds.list $(HOST_DIR)/share/zoneinfo
 endef
 
 $(eval $(generic-package))