packages: Fix build with libucl 0.9.3

In libucl 0.9.3, macros and includes are disabled by default when
creating a new UCL parser. This breaks the package build, which
relies on includes. Fix this by explicitly passing zero flags
to ucl.parser().

MFC after: 3 days
Fixes: abda442d92fd ("contrib/libucl: Import libucl 0.9.3")
Reviewed by: kevans, bapt
Reported by: freebsd@walstatt-de.de
Sponsored by: https://www.patreon.com/bsdivy
Differential Revision: https://reviews.freebsd.org/D56266