The python binary copied reports a valid signature on Big Sur and thus codesign fails.
Add the -f option so it overwrites the supposedly valid signature. Other versions are
either already unsigned or the install_name_tool invalidates the signature.
Make essential Tauthon's builtins and modules available in sandboxes, without
disrupting building with Python 2.7.
1. Allow new builtins and modules. "__build_class__" is for
building... new-style classes (to handle the new metaclass syntax imported from
3.x). "_oserror" is necessary because of internal changes to raise errors
deriving from OSError (which are reported as IOError if not caught).
2. Look for modules and packages in the right places.
This was tested on FreeBSD, and should work out of the box on Linux.