A number of Makefile fixes

- run-in-tempdir should depend on what it copies to the temporary dir
- Add PYTHON_BOOTSTRAP to BUILT_SOURCES
- Don't use “mkdir -p” directly
- Create directory if necessary for writing bootstrap script

In summary, this should make “make distcheck” in pristine
checkout work again.

Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>