Follow the path of what is done with bsnmp, build the modules along
with the main binary, this allows to build the modules at a moment
where all needed libraries are already built and available in the
linker path instead of having to declare all the libraries which a
flua module will be linked to in _prebuild_libs.
Discused with: markj
Reviewed by: markj, jrtc27, kevans, imp
Accepted by: kevans, imp
Differential Revision: https://reviews.freebsd.org/D46610
7899f917b1