Given Antoine's other change to the build process to fix the bootstrapping problem, I'm OK with leaving it up to anyone hacking on _bootstrap.py to remember that they need to run make if they want the interpreter to see any of their changes.
Unlike the C accelerator cases, it's not possible for the two implementations to get out of sync on the buildbots, so running the tests twice would just be a convenience change for anyone hacking on _bootstrap.py rather than being needed for correctness.
That said, if someone created a new issue and posted a patch to run the tests twice, I wouldn't object - a classic case of +0 :)