By Andrew Gray BRUSSELS, July 3 (Reuters) - NATO leaders gather next week in Ankara, where Europeans aim to set aside strife with U.S. President Donald Trump over Iran and Greenland and show they are stepping up to defend the continent as Washington cuts back on its commitments to the alliance. NATO Secretary General Mark Rutte says the gathering next Tuesday and Wednesday will show Europeans are honouring pledges to hike defence spending to deter Russia from any attack, with arms deals worth tens of billions of dollars to be signed.