gh-110968: Py_MOD_PER_INTERPRETER_GIL_SUPPORTED new in 3.13. (#110969)

gh-110968: Py_MOD_PER_INTERPRETER_GIL_SUPPORTED new in 3.13. (#110969)

* Only add Py_MOD_PER_INTERPRETER_GIL_SUPPORTED to limited C API
  version 3.13.
* errno, xxlimited and _ctypes_test extensions now need the limited C
  API version 3.13 to get Py_MOD_PER_INTERPRETER_GIL_SUPPORTED.  They
  now include standard header files explicitly: <errno.h>, <string.h>
  and <stdio.h>.
* xxlimited_35: Remove Py_mod_multiple_interpreters slot,
  incompatible with limited C API version 3.5.