"-a arch" is not requisite either; and having bunches
of empty lines in the resulting pkglists that are user
visible at least within the conventional installer's
alterator-pkg (groups selection) module wouldn't be nice.

I chose to sacrifice empty-line separators for clarity;
the really good cleanup would save *single* empty lines
between chunks of non-empty ones (not at the pkglist's
start or end); feel free to implement that as well.