Extract a script that massages Python scripts. This provides a couple of
benefits:
- The build logic is deduplicated across Make, CMake and Meson.
- CMake learns to rewrite scripts as-needed at build time instead of
only writing them at configure time.
Furthermore, we will use this script when introducing Meson to
deduplicate the logic across build systems.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>