swish-e fails to cross build from source, because the packaging does not
consider cross compilation and the way it performs the build manually
ends up building it for the build architecture. This manifests in three
areas:

1. Use of bare "gcc". For cross compilation, a triplet-prefixed tool
   should be used. An easy way to get the right one is including
   /usr/share/dpkg/buildtools.mk.
2. Failure to pass --build/--host flags to configure. The easiest way of
   doing so is using dh_auto_configure. That would mean refactoring
   debian/rules, so instead my patch suggests providing those flags
   explicitly.
3. Failure to export a cross PERL5LIB for building a Perl extension.
   Again dh_auto_configure would handle this automatically. Instead of
   refactoring debian/rules, my patch provides the variable explicitly.

Consider applying the attached patch and/or modernizing debian/rules.

Helmut