This fixes #277. Which is compensating for the change in debian

packaging behavior documented in
ros-infrastructure/buildfarm#197

We are using compat level 7 at the moment.  Compat level 9 seems to
deal with this automatically. Info from:
https://wiki.debian.org/HardeningWalkthrough#Enabling_dpkg-buildflags_in_your_debian.2Frules_files