https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61798
--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> --- Exit code 155 is indeed that the process has been killed by SIGPROF signal. Without a testcase there is hard to say anything more on this, libgomp certainly doesn't install a signal handler for this signal, nor generate it, nor do anything else with it, so I bet you'd get exactly the same situation if you just used pthread_create yourself instead of OpenMP.
