Placate -Wmissing-declarations in sim/cris

Placate -Wmissing-declarations in sim/cris

I get a couple of -Wmissing-declarations errors when building the sim.
This happens because an earlier patch added the declarations to a
cgen-generated header, but the recent re-generation then removed them.

This patch fixes the build by adding declarations just before the
definition.  This is normally not best practice, but in this
particular situation it at leat un-breaks the build.