bpo-34569: Fix subinterpreter 32-bit ABI, pystate.c/_new_long_object() (gh-9127)

This fixes ShareableTypeTests.test_int() in Lib/test/test__xxsubinterpreters.py.

Misc/NEWS.d/next/Tests/2018-09-09-14-36-59.bpo-34569.okj1Xh.rst

+The experimental PEP 554 data channels now correctly pass negative PyLong
+objects between subinterpreters on 32-bit systems. Patch by Michael Felt.

Python/pystate.c

@@ -1467,7 +1467,7 @@ _str_shared(PyObject *obj, _PyCrossInterpreterData *data)
 static PyObject *
 _new_long_object(_PyCrossInterpreterData *data)
 {
-    return PyLong_FromLongLong((int64_t)(data->data));
+    return PyLong_FromLongLong((intptr_t)(data->data));
 }
 
 static int