Make it so the tmpfs plugin doesn't load on FreeBSD.

The mount command relies on bind mounting and being able to
create private mounts and bind mount namespaces to it.  At the time of
writing this it doesn't work there.

Bug 8993

src/plugins/job_container/tmpfs/job_container_tmpfs.c

@@ -134,6 +134,10 @@ extern void container_p_reconfig(void)
  */
 extern int init(void)
 {
+#if defined(__APPLE__) || defined(__FreeBSD__)
+	fatal("%s is not available on this system. (mount bind limitation)", plugin_name);
+#endif
+
 	debug("%s loaded", plugin_name);
 
 	return SLURM_SUCCESS;
@@ -233,6 +237,7 @@ extern int container_p_restore(char *dir_name, bool recover)
 		return SLURM_ERROR;
 	}
 
+#if !defined(__APPLE__) && !defined(__FreeBSD__)
 	/*
 	 * MS_BIND mountflag would make mount() ignore all other mountflags
 	 * except MS_REC. We need MS_PRIVATE mountflag as well to make the
@@ -251,6 +256,7 @@ extern int container_p_restore(char *dir_name, bool recover)
 		      __func__, strerror(errno));
 		return SLURM_ERROR;
 	}
+#endif
 	debug3("tmpfs: Base namespace created");
 
 	return SLURM_SUCCESS;
@@ -262,6 +268,7 @@ static int _mount_private_tmp(char *path)
 		error("%s: cannot mount /tmp", __func__);
 		return -1;
 	}
+#if !defined(__APPLE__) && !defined(__FreeBSD__)
 	if (mount(NULL, "/", NULL, MS_PRIVATE|MS_REC, NULL)) {
 		error("%s: making root private: failed: %s",
 		      __func__, strerror(errno));
@@ -272,7 +279,7 @@ static int _mount_private_tmp(char *path)
 		      __func__, strerror(errno));
 		return -1;
 	}
-
+#endif
 	return 0;
 }
 
@@ -286,12 +293,14 @@ static int _mount_private_shm(void)
 		      __func__, strerror(errno));
 		return rc;
 	}
+#if !defined(__APPLE__) && !defined(__FreeBSD__)
 	rc = mount("tmpfs", "/dev/shm", "tmpfs", 0, NULL);
 	if (rc) {
 		error("%s: mounting private /dev/shm failed: %s\n",
 		      __func__, strerror(errno));
 		return -1;
 	}
+#endif
 	return rc;
 }
 
@@ -511,6 +520,7 @@ extern int container_p_create(uint32_t job_id)
 		 * Bind mount /proc/pid/ns/mnt to hold namespace active
 		 * without a process attached to it
 		 */
+#if !defined(__APPLE__) && !defined(__FreeBSD__)
 		rc = mount(proc_path, ns_holder, NULL, MS_BIND, NULL);
 		if (rc) {
 			error("%s: ns base mount failed: %s",
@@ -520,6 +530,7 @@ extern int container_p_create(uint32_t job_id)
 				      __func__, strerror(errno));
 			goto exit1;
 		}
+#endif
 		if (sem_post(sem2) < 0) {
 			error("%s: sem_post failed: %s",
 			      __func__, strerror(errno));