Code generation saved files even when they had not changed, which often caused code generation cascades. So, don't save files unless they have changed.
Use rsync to determine which files have changed since the last test run. The manifest of changed files is saved and not removed until all code generation and builds have completed. If an error occurs the work will be redone on the next run.
The eventual goal is to do all the builds from the test/repo directory created by rsync but for now it is only used to track changes.
Improve on 7794ab50 by including the build flag files directly into the Makefile as dependencies (even though they are not includes). This simplifies some of the rsync logic and allows make to do what it does best.
Also split build flag files into test, harness, and build to reduce rebuilds. Test flags are used to build test.c, harness flags are used to build the rest of the files in the test harness, and build flags are used for the files that are not directly involved in testing.
