CPACK fix (HWLOC dependency missing)

This MR adds hwloc as a dependency to the DEB package --- as the release packages of the compiler include hwloc by default (it is activated automatically when using mt_pth), the user needs to have this installed. The instructions on sac-home.org stipulate this, but it helps if we make it hard dependency through the DEB.

RPM is all right, as CPACK's internal calls to rpmbuild pull in the correct dependencies. Unfortunately create a DEB is not as streamlined.