pysmbc fails to cross build for a number of reasons.

On the surface, it's python3-pytest dependency is not satisfiable. One
would expect it to not be needed during cross builds and indeed,
annotating it <!nocheck> gets rid of it without affecting binary output.

Then, the python3-all-dev dependency needs to be converted for cross
compilation. It becomes "python3-all-dev:any, libpython3-all-dev".

Last but not least, setup.py hard codes the build architecture
pkg-config and therefore fails finding required packages. I propose
making it substitable via the environment and providing a suitable
substitution.

You may find all of the proposed changes in the attached debdiff. Once
applying it, pysmbc becomes cross buildable.

Helmut