bpo-30638: Add clinic to `make regen-all` (GH-5671)


Also, use PYTHON_FOR_REGEN for clinic and blake2s_impl.c rather than PYTHON_FOR_BUILD, and update .travis.yml to make use of the change.
(cherry picked from commit d6ff8a7037903497eff95fa32bdac2b6adf71505)

Co-authored-by: Zachary Ware <zachary.ware@gmail.com>
2 files changed