- Check that libmbedcrypto was not built at the top level.
- Check that we've built libmbedcrypto with the correct files. Build
libmbedcrypto with debug symbols and verify that files used are from the
crypto submodule.
- Check that config.h is handled properly. Enable a feature at the top
level that the crypto library submodule has disabled in its config.h, and
check that the library symboles indicate that the feature is present in
libmbedcrypto.
- Ensure basic functionality of the resulting build with a run of
`make test` and `ssl-opt.sh`.