bpo-38588: Optimize list comparison. (GH-17766)

Mitigate performance regression of the list comparison caused by 2d5bf56.

Objects/listobject.c

@@ -2664,6 +2664,9 @@ list_richcompare(PyObject *v, PyObject *w, int op)
     for (i = 0; i < Py_SIZE(vl) && i < Py_SIZE(wl); i++) {
         PyObject *vitem = vl->ob_item[i];
         PyObject *witem = wl->ob_item[i];
+        if (vitem == witem) {
+            continue;
+        }
 
         Py_INCREF(vitem);
         Py_INCREF(witem);