Enforce a 'strict dependencies' mode where implicit dependencies are disabled
SB3 build should decide whether system libraries are required or provided.
- Required libraries always have to be present for the builds that depend on them
- Provided libraries are never present on the system, to avoid collateral dependencies. -- Build should not proceed if it may accidentally link to a system library (e.g. HDF5, netCDF4).
Ideally there's going to be warning well ahead of mid-build that the build system is broken.
Not sure whether this scopes us into another build system, e.g. buildout/autoconf.