bpo-43372: Use _freeze_importlib for regen-frozen. (GH-24759)

This approach ensures the code matches the interpreter version.
Previously, PYTHON_FOR_REGEN was used to generate the code, which might
be wrong. The marshal format for code objects has changed with
bpo-42246, commit 877df851. Update the code and the expected code sizes
in ctypes test_frozentable.