Fix build errors on recent macOS versions.

[icemac]

Traceback without these changes

py311: packaging backend failed (code=error: command '/usr/bin/clang' failed with exit code 1), with SystemExit: error: command '/usr/bin/clang' failed with exit code 1
src/AccessControl/cAccessControl.c:428:2: error: incompatible pointer to integer conversion initializing 'Py_ssize_t' (aka 'long') with an expression of type 'void *'
      [-Wint-conversion]
        NULL,                                   /* tp_print     */
        ^~~~
/Library/Developer/CommandLineTools/SDKs/MacOSX14.sdk/usr/include/sys/_types/_null.h:30:15: note: expanded from macro 'NULL'
#define NULL  __DARWIN_NULL
              ^~~~~~~~~~~~~
/Library/Developer/CommandLineTools/SDKs/MacOSX14.sdk/usr/include/sys/_types.h:52:23: note: expanded from macro '__DARWIN_NULL'
#define __DARWIN_NULL ((void *)0)
                      ^~~~~~~~~~~
src/AccessControl/cAccessControl.c:487:2: error: incompatible pointer to integer conversion initializing 'Py_ssize_t' (aka 'long') with an expression of type 'void *'
      [-Wint-conversion]
        NULL,                                   /* tp_print     */
        ^~~~
/Library/Developer/CommandLineTools/SDKs/MacOSX14.sdk/usr/include/sys/_types/_null.h:30:15: note: expanded from macro 'NULL'
#define NULL  __DARWIN_NULL
              ^~~~~~~~~~~~~
/Library/Developer/CommandLineTools/SDKs/MacOSX14.sdk/usr/include/sys/_types.h:52:23: note: expanded from macro '__DARWIN_NULL'
#define __DARWIN_NULL ((void *)0)
                      ^~~~~~~~~~~
src/AccessControl/cAccessControl.c:546:2: error: incompatible pointer to integer conversion initializing 'Py_ssize_t' (aka 'long') with an expression of type 'void *'
      [-Wint-conversion]
        NULL,                                   /* tp_print     */
        ^~~~
/Library/Developer/CommandLineTools/SDKs/MacOSX14.sdk/usr/include/sys/_types/_null.h:30:15: note: expanded from macro 'NULL'
#define NULL  __DARWIN_NULL
              ^~~~~~~~~~~~~
/Library/Developer/CommandLineTools/SDKs/MacOSX14.sdk/usr/include/sys/_types.h:52:23: note: expanded from macro '__DARWIN_NULL'
#define __DARWIN_NULL ((void *)0)
                      ^~~~~~~~~~~
src/AccessControl/cAccessControl.c:616:2: error: incompatible pointer to integer conversion initializing 'Py_ssize_t' (aka 'long') with an expression of type 'void *'
      [-Wint-conversion]
        NULL,                                   /* tp_print     */
        ^~~~
/Library/Developer/CommandLineTools/SDKs/MacOSX14.sdk/usr/include/sys/_types/_null.h:30:15: note: expanded from macro 'NULL'
#define NULL  __DARWIN_NULL
              ^~~~~~~~~~~~~
/Library/Developer/CommandLineTools/SDKs/MacOSX14.sdk/usr/include/sys/_types.h:52:23: note: expanded from macro '__DARWIN_NULL'
#define __DARWIN_NULL ((void *)0)
                      ^~~~~~~~~~~
4 errors generated.

I am running on Sonoma 14.4.1 on an Apple chip.

The PyExtensionClass is actually a PyTypeObject and the examples in the Python docs also use a 0 here instead of NULL: https://docs.python.org/3/c-api/typeobj.html#typedef-examples

[icemac]

I have no idea about the failures when pushing to coveralls.

[icemac]

I also saw the coveralls errors in zope.deprecation, so I created TheKevJames/coveralls-python#440

[d-maurer]

Python 3.8+ has reused the slot used for tp_print in Python 2 (and therefore had as type a function pointer) as tp_vectorcall_offset (now a size slot).

I suggest to not only use a type correct initializer for the slot but also change the explanatory comment.

[icemac]

@d-maurer Thank you for your suggestions, could you please re-review?