configury: fix pthread flags for fortran

(cherry picked from commit open-mpi/ompi@8976dcf)

Author: ggouaillardet

config/ompi_config_pthreads.m4

@@ -114,6 +114,7 @@ void pthreadtest_f(void)
     pthread_attr_t attr;
 
     me = pthread_self(); 
+    pthread_atfork(NULL, NULL, NULL);
     pthread_attr_init(&attr); 
     pthread_cleanup_push(cleanup_routine, 0);
     pthread_create(&newthread, &attr, thread_main, 0);