The run_tests.py script's CLanguage should load build.json and parse the list of the tests to run.

In build.json, the array targets can have objects with the following properties:

"c++" set to true or false; if not set, default to false.
"run" set to true or false; if not set, default to true.

So, the code should select the appropriate tests to run, based on the language tag, and based on the fact it's a test that needs to be run.

Note that we will probably need to extend the build.json file to include the notion of complex tests - aka, tests that run off a shell script or something similar, and that execute several binaries with arguments.