McDONALD'S may serve Happy Meals at its 30,000 sites around the globe, but it's a pretty safe bet that meal times — and the hours in between — are less than joyful at the company's headquarters in Oak Brook, Ill. Customers are defecting, franchisees are complaining, and shareholders are fleeing. Mention the Golden Arches on Wall Street, and be prepared for a bunch of "fallen arches" jokes. Jack M. Greenberg, the chief executive of McDonald's, and his team have tried just about everything to bolster the company's sales, profits and share price. They have bought chains like Chipotle Mexican Grill,...