LONDON (Reuters) - Global shares eked out gains on Tuesday as some investors held out hopes for a trade deal between the United States and China, even as the countries continued to raise tariffs on each other last week.Shares in Asia gained following a rise in U.S. stocks on Monday, which came after U.S. President Donald Trump predicted a trade deal with China. The optimism didn't carry over to Europe however, with most major country share indices down in early deals.Britain's FTSE 100 index ..