This is almost certainly caused by https://bugs.gentoo.org/667512 but Icedtea 3.9.0 is failing to build with a configure error because it can't find netinet/sctp.h There was a file netinet/sctp.h.in belonging to net-misc/lksctp-tools Renaming that file to sctp.h or rolling net-misc/lksctp-tools back to 1.0.17 (from 1.0.18) fixes the problem.
Yes, except in the unlikely event that this turns out to be expected lksctp-tools behaviour, I don't see us changing anything in IcedTea.
Should this be marked as a duplicate of bug #667512? Or at least depend on it?
Bug #667512 has dealt with this.