Move IRC config into a proper build file.

Using project('irc') doesn't work properly in a multiproject env.

Change-Id: Id4fd006efa7802e7972bf9f21c60d41ef48bceae
Reviewed-on: http://gerrit.dmdirc.com/4086
Automatic-Compile: DMDirc Build Manager
Reviewed-by: Greg Holmes <greg@dmdirc.com>