use the static identifier api for looking up special methods

I had to move the static identifier code from unicodeobject.h to object.h in
order for this to work.
diff --git a/Objects/complexobject.c b/Objects/complexobject.c
index 1e61b96..b73dc4b 100644
--- a/Objects/complexobject.c
+++ b/Objects/complexobject.c
@@ -265,9 +265,9 @@
 static PyObject *
 try_complex_special_method(PyObject *op) {
     PyObject *f;
-    static PyObject *complexstr;
+    _Py_IDENTIFIER(__complex__);
 
-    f = _PyObject_LookupSpecial(op, "__complex__", &complexstr);
+    f = _PyObject_LookupSpecial(op, &PyId___complex__);
     if (f) {
         PyObject *res = PyObject_CallFunctionObjArgs(f, NULL);
         Py_DECREF(f);