in configure.in we can see that an optional dependencie on media-libs/libiec61883 in order to enable firewire support I think. I will post a patch that should fix this, but since I do not use firewire, I can't really test it.
Created attachment 151677 [details, diff] patch to fix the automagic dependencie The default behavior is not change by the patch. It will test for libiec61883. But if we call configure with --without-libiec61883 it won't build this.
Created attachment 151678 [details, diff] patch to enable the new use flag
applied, thanks ! Please note that it needs to patch configure.in.in because its regenerated from there.