By Andrew Gray ANKARA, July 7 (Reuters) - NATO leaders plan to unveil arms deals worth tens of billions of dollars in Ankara on Tuesday to show they are heeding U.S. calls to spend more to defend Europe before joining President Donald Trump for a summit. European governments will announce the deals at a NATO defence industry forum before Trump flies in to meet Turkish President Tayyip Erdogan and join fellow leaders of the military alliance for the summit, which begins with a dinner on Tuesday e