[issue29300] Modify the _struct module to use FASTCALL and Argument Clinic

[Serhiy Storchaka]

Serhiy Storchaka added the comment:

unpack_buffer.patch LGTM. Please backport test changes and other changes discussed before to other branches.

----------

_______________________________________
Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue29300>
_______________________________________