Add an index entry for exec() builtin.

Reported by Draic Kin on docs@.
Merge from 3.4.
Issue #21892, #21893: Partial revert of changeset 4f55e802baf0, PyErr_Format()
uses "%zd" for Py_ssize_t, not PY_FORMAT_SIZE_T
(Merge 3.4) Issue #21892, #21893: Partial revert of changeset 4f55e802baf0,
PyErr_Format() uses "%zd" for Py_ssize_t, not PY_FORMAT_SIZE_T
properly decref the return value of close()
properly decref the return value of close()
merge 3.4
Issue #21897: Fix a crash with the f_locals attribute with closure variables when frame.clear() has been called.
Issue #21897: Fix a crash with the f_locals attribute with closure variables when frame.clear() has been called.