Yes its using openMP. Two of my object files were referred to as callees for the missing __tgt... things and each is using do concurrent, but not within a parallel region. Reverting to serial loops eliminated the issue.
I tried to make a small re-producer with same project settings and use of do concurrent but it didn't replicate the link issue.
My use of do concurrent was questionable, it was done when this construct started to be supported and well before it was parallelised by the compiler. It is no benefit since the work in the loop was too small to justify the overhead of starting up threads so its simplest for me to change these to serial loops.
New discovery is that the original link error only occurred in my debug build. Maybe the do concurrent was not parallelised in the release build because of the small amount of work seen by the optimiser.
