tests/kernel: Add a test for CONFIG_MULTITHREADING=n

This is a feature Ben added so you could use Zephyr's arch layer to
bootstrap things like bootloaders without sucking in the whole kernel.
And it's worked until now.

But we never had a test for it, and I just broke it with the scheduler
rework.  Add a trivial test just to make sure this continues to link
and run.  Longer term it would be nice to have some kind of size
metric here to guarantee that the feature stays lean and doesn't pull
in needless code.

Signed-off-by: Andy Ross <andrew.j.ross@intel.com>
4 files changed