Loss of stdout for prif_error_stop and quiet prif_stop on distributed conduits

[bonachea]

Testing with Caffeine and flang 21 on distributed conduits (udp and ofi) reveals that we are sometimes losing final output from the caller that might be buffered in the Fortran-level output_unit, most commonly in jobs that end in prif_error_stop or prif_stop(quiet=.true.).