Please check this, there is no configure option and a brief glace looks like it is automagic. Thanks.
There should not be an expat USE flag. Expat is a required dependency since SVN r1658[1]. This change was committed during the development of 0.11.0. I must have missed this in my original 0.11.0 ebuild. [1] http://mediatomb.svn.sourceforge.net/viewvc/mediatomb?view=rev&revision=1658
fixed