dist/ubuntu: add missing build time dependency for libunwind
dist/ubuntu: add missing build time dependency for libunwind

There was missing dependency for libunwind, so add it.
Fixes #1721

Signed-off-by: Takuya ASADA <4ebfb6f510af412d6e89fefa3ab96d9c8b5e3fff@scylladb.com>
Message-Id: <1475255706-26434-1-git-send-email-4ebfb6f510af412d6e89fefa3ab96d9c8b5e3fff@scylladb.com>

duarten/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla,scylladb/scylla,raphaelsc/scylla,raphaelsc/scylla,avikivity/scylla,raphaelsc/scylla,duarten/scylla,avikivity/scylla,duarten/scylla,avikivity/scylla