EMERGING MARKETS-Mexican stocks lead region, end yr up 17.88 pct

* Mexico IPC finisheds flat for day on Monday * Brazilian and Chilean markets closed on Monday * Markets await "fiscal cliff" deal By Gabriel Stargardter MEXICO CITY, Dec 31 (Reuters) - Mexico's IPC stock index ended the year up 17.88 percent, significantly outperforming Brazil's Bovespa, as Mexico benefits from its proximity to an improving U.S. economy and hopes about potential domestic reforms. Following last minute wranglings over the U.S. "fiscal cliff," the IPC ended