archivers/py-zlib-ng: Add an option to use zlib-ng from ports instead of bundled version

Our archivers/zlib-ng version is newer than bundled one so let's add an
option to use it instead of bunlded version (off by default).
Maybe we'll switch default to archivers/zlib-ng later.

PR:	284470

archivers/py-zlib-ng/Makefile

@@ -19,6 +19,13 @@ BUILD_DEPENDS=	${PYTHON_PKGNAMEPREFIX}setuptools>=51:devel/py-setuptools@${PY_FL
 USES=		cmake:indirect python
 USE_PYTHON=	autoplist pep517
 
+OPTIONS_DEFINE=			SYSTEM_ZLIB_NG
+
+SYSTEM_ZLIB_NG_DESC=		Use archivers/zlib-ng instead of bundled version
+
+SYSTEM_ZLIB_NG_LIB_DEPENDS=	libz-ng.so:archivers/zlib-ng
+SYSTEM_ZLIB_NG_MAKE_ENV=	PYTHON_ZLIB_NG_LINK_DYNAMIC=1
+
 post-install:
 	${STRIP_CMD} ${STAGEDIR}${PYTHON_SITELIBDIR}/${PORTNAME:S/-/_/}/${PORTNAME:S/-/_/}.cpython-${PYTHON_VER:S/.//}.so