GLOBAL MARKETS-Shares flat on earnings, oil jumps on Middle East worry

* European shares slide after soft PMIs * U.S. stocks flat with focus on earnings * Oil rises on Middle East concern (Updates to U.S. market open, changes byline, changes dateline, previous London) By Chuck Mikolajczak NEW YORK, April 23 (Reuters) - Stocks in major markets shook off soft data in big economies to hold near the unchanged mark on Thursday, while oil prices climbed on Middle East tensions. U.S. stocks were little changed. Some strong earnings from AT&T, up