Pass PYTHON_FOR_REGEN to python build and build from a copy of the sources am: 1e56abcdc9 am: bbb77c498f

Original change: https://googleplex-android-review.googlesource.com/c/platform/external/python/cpython3/+/38244690

Change-Id: I14b51c3633bc100f3fd8438c3faa7c7c30fc5fa0
Signed-off-by: Automerger Merge Worker <[email protected]>