Several parts of the code need boost_system, but don't explicitly
add it to their respective linker commands. This causes the build to fail when
--no-copy-dt-needed entries is set, so add them to the command line.
The -Wl,--no-as-needed flag is a workaround for cgsl being underlinked, causing a
build failure in Ubuntu, where --as-needed is set as default. Arguably, this
should be resolved in cgsl, but in the meantime, this is a good workaround.

Debian bug: http://bugs.debian.org/720821