fix some C warnings about unused variables and ambiguous operators

Closes #1506

Cython/Utility/ObjectHandling.c

@@ -1639,11 +1639,9 @@ static CYTHON_INLINE PyObject * __Pyx_PyCFunction_FastCall(PyObject *func_obj, P
     PyCFunctionObject *func = (PyCFunctionObject*)func_obj;
     PyCFunction meth = PyCFunction_GET_FUNCTION(func);
     PyObject *self = PyCFunction_GET_SELF(func);
-    PyObject *result;
-    int flags;
 
     assert(PyCFunction_Check(func));
-    assert(METH_FASTCALL == PyCFunction_GET_FLAGS(func) & ~(METH_CLASS | METH_STATIC | METH_COEXIST));
+    assert(METH_FASTCALL == (PyCFunction_GET_FLAGS(func) & ~(METH_CLASS | METH_STATIC | METH_COEXIST)));
     assert(nargs >= 0);
     assert(nargs == 0 || args != NULL);