jool fails to cross build from source, because it builds its iptables
extension for the build architecture. It's an autoconf/automake project,
but the src/usr/iptables directory contains a bare Makefile. It is this
hand-off where the toolchain is lost as automake expects each Makefile
to be aware of the toolchain, but this one isn't.

I propose using the "-local" hook mechanism to run the submake
explicitly and thus be able to pass the toolchain. This is implemented
in the attached patch and it makes jool cross buildable. Please consider
applying it and forwarding it upstream as it also helps other Linux
distributions.

Helmut