In reply to John Nairn.

Given the status of plugins in Xcode 8, I don't see this (your solution) as viable moving forward. If you look at the Stack Overflow link I posted above, there are additional comments on how to get this working (via MacPorts) with Xcode 8 (posted Dec 2016).

Using OpenMP in Xcode was always just a curiosity for me, if I need serious (parallel) performance, I'll write the code in C/C++ and just run it from the command line.