package/ngircd: make zlib an optional dependency

zlib is not a hard dependency:
https://github.com/ngircd/ngircd/blob/master/configure.ng#L256

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>

package/ngircd/Config.in

@@ -1,7 +1,6 @@
 config BR2_PACKAGE_NGIRCD
 	bool "ngircd"
 	depends on BR2_USE_MMU # fork()
-	select BR2_PACKAGE_ZLIB
 	help
 	  Next Generation IRC server deamon.
 

package/ngircd/ngircd.mk

@@ -7,7 +7,6 @@
 NGIRCD_VERSION = 24
 NGIRCD_SOURCE = ngircd-$(NGIRCD_VERSION).tar.xz
 NGIRCD_SITE = https://arthur.barton.de/pub/ngircd
-NGIRCD_DEPENDENCIES = zlib
 NGIRCD_LICENSE = GPL-2.0+
 NGIRCD_LICENSE_FILES = COPYING
 
@@ -24,4 +23,11 @@ NGIRCD_CONF_OPTS += --without-gnutls
 endif
 endif
 
+ifeq ($(BR2_PACKAGE_ZLIB),y)
+NGIRCD_CONF_OPTS += --with-zlib=$(STAGING_DIR)/usr
+NGIRCD_DEPENDENCIES += zlib
+else
+NGIRCD_CONF_OPTS += --without-zlib
+endif
+
 $(eval $(autotools-package))