Thanks for the patch and sorry for the long delay in replying.  As you may know, as of Python 3.7, we no longer "vendor" a copy of the libffi source in Python source releases; you now have to use either a system-supplied version of libffi or otherwise supply your own copy of the library.  So, if the changes to libffi are still needed, you would need to pursue them with the libffi project.