A number of ebuilds failed repeatedly until I added MAKEOPTS="-j1" to /etc/make.conf net-dns/bind-tools-9.2.1 net-dns/bind-9.2.1 dev-util/kdevelop-2.1.1 bind in particular recommends not using a parallel make in its README This is using portage 2.0.15
bind has an -r1 out already which uses single make, and kdevelop isn't compiled at all, from what I see in the ebuild. referring to verwilst for that.
kdevelop-2.1.2 and later introduced MAKEOPTS+=-j1. So this is fixed.