cext: match format string for 32bit long platforms

cext: match format string for 32bit long platforms

Differential Revision: https://phab.mercurial-scm.org/D9546

--- a/mercurial/cext/revlog.c	Tue Dec 08 13:33:40 2020 -0800
+++ b/mercurial/cext/revlog.c	Tue Dec 08 23:01:24 2020 +0100
@@ -370,7 +370,7 @@
 
 static PyObject *index_append(indexObject *self, PyObject *obj)
 {
-	unsigned long offset_flags;
+	uint64_t offset_flags;
 	int rev, comp_len, uncomp_len, base_rev, link_rev, parent_1, parent_2;
 	Py_ssize_t c_node_id_len;
 	const char *c_node_id;