bpo-35444: Unify and optimize the helper for getting a builtin object. (GH-11047)

This speeds up pickling of some iterators.

This fixes also error handling in pickling methods when fail to
look up builtin "getattr".
diff --git a/Objects/classobject.c b/Objects/classobject.c
index 1eed5d3..0d1cf7a 100644
--- a/Objects/classobject.c
+++ b/Objects/classobject.c
@@ -78,8 +78,6 @@
 {
     PyObject *self = PyMethod_GET_SELF(im);
     PyObject *func = PyMethod_GET_FUNCTION(im);
-    PyObject *builtins;
-    PyObject *getattr;
     PyObject *funcname;
     _Py_IDENTIFIER(getattr);
 
@@ -87,9 +85,8 @@
     if (funcname == NULL) {
         return NULL;
     }
-    builtins = PyEval_GetBuiltins();
-    getattr = _PyDict_GetItemId(builtins, &PyId_getattr);
-    return Py_BuildValue("O(ON)", getattr, self, funcname);
+    return Py_BuildValue("N(ON)", _PyEval_GetBuiltinId(&PyId_getattr),
+                         self, funcname);
 }
 
 static PyMethodDef method_methods[] = {