libmysqlclient-dev (or libmariadbclient-dev) is needed to build Fail*.
A running MySQL/MariaDB server to talk to is needed for the
fault-space pruning tools and the DatabaseCampaign, too, but that's a
runtime dependency.

Change-Id: I1f7fbdaf20b49370039e8d27a07a8785e0f052b5