s_methods[]: Stop compiler warnings by casting

s_unpack_from to PyCFunction.

Modules/_struct.c

@@ -1669,7 +1669,8 @@ static struct PyMethodDef s_methods[] = {
 	{"pack",	s_pack,		METH_VARARGS, s_pack__doc__},
 	{"pack_into",	s_pack_into,	METH_VARARGS, s_pack_into__doc__},
 	{"unpack",	s_unpack,       METH_O, s_unpack__doc__},
-	{"unpack_from",	s_unpack_from,	METH_KEYWORDS, s_unpack_from__doc__},
+	{"unpack_from",	(PyCFunction)s_unpack_from, METH_KEYWORDS,
+			s_unpack_from__doc__},
 	{NULL,	 NULL}		/* sentinel */
 };