And I bet you are running Xcode 9? There was an issue with Xcode 9, that was fixed in version 6.10.08. I see other complaining about the same error message for different projects when moving to Xcode 9. Why don’t you give that version a try and see if you still have issues.
https://root.cern.ch/doc/v610/release-notes.html#release-6.1008
https://sft.its.cern.ch/jira/browse/ROOT-9015