revlog: add a comment to help clang-format produce less-awful results

Differential Revision: https://phab.mercurial-scm.org/D5232

mercurial/cext/revlog.c

@@ -51,7 +51,7 b' typedef struct {'
 } nodetree;
 
 typedef struct {
-	PyObject_HEAD
+	PyObject_HEAD /* ; */
 	nodetree nt;
 } nodetreeObject;