Silence expression result unused warnings with clang.

The PyObject_INIT() macros returns obj:

../cpython/Objects/methodobject.c:32:23: warning: expression result unused [-Wunused-value]
        PyObject_INIT(op, &PyCFunction_Type);
                      ^~
../cpython/Include/objimpl.h:139:69: note: expanded from macro 'PyObject_INIT'
    ( Py_TYPE(op) = (typeobj), _Py_NewReference((PyObject *)(op)), (op) )
                                                                    ^
1 warning generated.