bpo-41085: Fix array.array.index() on 64-bit Windows (GH-21071)

Fix integer overflow in the :meth:`array.array.index` method on 64-bit Windows
for index larger than ``2**31``.
(cherry picked from commit 1d3dad5f96)

Co-authored-by: WildCard65 <WildCard65@users.noreply.github.com>

Misc/NEWS.d/next/Tests/2020-06-23-12-02-45.bpo-41085.JZKsyz.rst

@@ -0,0 +1,2 @@
+Fix integer overflow in the :meth:`array.array.index` method on 64-bit Windows
+for index larger than ``2**31``.

Modules/arraymodule.c

@@ -1141,7 +1141,7 @@ array_array_index(arrayobject *self, PyObject *v)
         cmp = PyObject_RichCompareBool(selfi, v, Py_EQ);
         Py_DECREF(selfi);
         if (cmp > 0) {
-            return PyLong_FromLong((long)i);
+            return PyLong_FromSsize_t(i);
         }
         else if (cmp < 0)
             return NULL;