sim: testsuite: push $arch out to targets

sim: testsuite: push $arch out to targets

This is needed to move to automake & its dejagnu-provided logic,
and eventually by the unified sim logic.  The $arch is used only
to figure out which `run` program to use when running tests, and
as we move to a single top-level build, we can delete this and
use sim/run directly.