work around 'unused function __Pyx_ImportModule()' compiler warning

Cython/Compiler/ModuleNode.py

@@ -1912,12 +1912,9 @@ class ModuleNode(Nodes.Node, Nodes.BlockNode):
         self.body.generate_execution_code(code)
 
         if Options.generate_cleanup_code:
-            # this should be replaced by the module's tp_clear in Py3
             code.globalstate.use_utility_code(
                 UtilityCode.load_cached("RegisterModuleCleanup", "ModuleSetupCode.c"))
-            code.putln("#if PY_MAJOR_VERSION < 3")
             code.putln("if (__Pyx_RegisterCleanup()) %s;" % code.error_goto(self.pos))
-            code.putln("#endif")
 
         code.put_goto(code.return_label)
         code.put_label(code.error_label)

Cython/Utility/ModuleSetupCode.c

@@ -478,8 +478,8 @@ end:
 /////////////// RegisterModuleCleanup.proto ///////////////
 //@substitute: naming
 
-#if PY_MAJOR_VERSION < 3
 static int __Pyx_RegisterCleanup(void); /*proto*/
+#if PY_MAJOR_VERSION < 3
 static PyObject* ${cleanup_cname}(PyObject *self, PyObject *unused); /*proto*/
 #endif
 
@@ -552,4 +552,10 @@ bad:
     Py_XDECREF(res);
     return ret;
 }
+#else
+// fake call purely to work around "unused function" warning for __Pyx_ImportModule()
+static int __Pyx_RegisterCleanup(void) {
+    if (0) __Pyx_ImportModule(NULL);
+    return 0;
+}
 #endif