Cross-platform detection of multiarch

[Jan Medlock <medlock-debian@turboshower.net>]

What is the recommended way to detect the presence of multiarch in a
cross-platform build?

I'm trying to fix up the Sage <http://www.sagemath.org/> build, which
seems to need to set a search path on multiarch systems:
<http://trac.sagemath.org/sage_trac/ticket/11243>

Currently, there's an explicit check for Ubuntu 11.04, which doesn't
work for Debian and its other derivatives, will break with the next
version of Ubuntu, etc.

So, what's the best way to check whether the OS has multiarch?

I though about using dpkg-architecture.  Another way would be
preferred since dpkg-dev, the package containing dpkg-architecture,
might not be installed.

Thanks,
Jan Medlock