build.sh: change working directory to "$(dirname "${0}")" at startup.
    etc/build.usage: updated.
    groups/2*.native_packages_*.group: adds dependencies.
    vars/env.vars, groups/{010.host_deps,120.native_runtime}.group: removes ${PKG_SRC_TARBALL_DISABLE}.
    groups/999.invariants.group b, vars/{env,invariants_tarballs}.vars: removes tarball generation.
    subr/build_args.subr: reimplemented using getopts(1).
    subr/{build_args,ex_pkg_dispatch}.subr: don't inhibit dependency processing if ${ARG_RESTART_RECURSIVE} is set.