July 25 (Reuters) - A profit warning by Walmart WMT.N ignited a sell-off in shares of major U.S. retailers late on Monday, quickly evaporating over $100 billion in stock market value in extended trade. Sounding an alarm that inflation is hurting its shoppers and forcing them to change what they spend on, Walmart cut its forecast for full-year profit, saying it expects its adjusted earnings per share to drop as much as 13%. That change in consumer spending has forced Walmart to cut prices on items like apparel in order to reduce its inventory.