We should document what external dependencies we assume for our test suites

Location

The test suites, especially tests/run-make and tests/run-make-fulldeps.

Summary

It'd be nice for people to be able to reliably run test suites without necessarily having to rely on Docker environments, or at least know what external dependencies are assumed to be available (and what version/flavor as well) by the test suites. This is also relevant for people trying to work on or maintain new targets if they want to run the test suites. Example dependencies (non-exhaustive, have not fully surveyed):

• Utilities: e.g. nm, grep.
• C/C++ compilers, e.g. what cc points to is a massive pain.
• Python: again, which python version is also a massive pain.
• Make and makefiles: we're trying to escape from this
• Shell: bash? or what do the various bash scripts assume?

For example, the run-make test suite has a bunch of assumed external dependencies (like nm) which are not documented AFAICT.

Start by surveying the test suites in tests/run-make and tests/run-make-fulldeps, including their scripts and makefiles. Identify assumed utilities, compilers, Python and shell versions or flavors, then document those dependencies and target-specific requirements. Done means contributors can determine what external tools and versions are needed without relying on Docker.