Issue #15989: Fix several occurrences of integer overflow
when result of PyLong_AsLong() narrowed to int without checks.

This is a backport of changesets 13e2e44db99d and 525407d89277.
diff --git a/Include/longobject.h b/Include/longobject.h
index c09565a..5f8b178 100644
--- a/Include/longobject.h
+++ b/Include/longobject.h
@@ -26,6 +26,9 @@
 PyAPI_FUNC(size_t) PyLong_AsSize_t(PyObject *);
 PyAPI_FUNC(unsigned long) PyLong_AsUnsignedLong(PyObject *);
 PyAPI_FUNC(unsigned long) PyLong_AsUnsignedLongMask(PyObject *);
+#ifndef Py_LIMITED_API
+PyAPI_FUNC(int) _PyLong_AsInt(PyObject *);
+#endif
 PyAPI_FUNC(PyObject *) PyLong_GetInfo(void);
 
 /* It may be useful in the future. I've added it in the PyInt -> PyLong