Add some handling to remaining unlinkat calls

Coverity now started warning about this ("Calling unlinkat without checking
return value (as is done elsewhere 12 out of 15 times).", and it is right:
most of the time we should at list print a log message so people can figure
out something is wrong when this happens.

v2:
- use warning level in journald too (this is unlikely to happen ever, so it
  should be safe to something that is visible by default).

src/journal/journald-stream.c

@@ -778,7 +778,9 @@ int server_restore_streams(Server *s, FDSet *fds) {
                 if (!found) {
                         /* No file descriptor? Then let's delete the state file */
                         log_debug("Cannot restore stream file %s", de->d_name);
-                        unlinkat(dirfd(d), de->d_name, 0);
+                        if (unlinkat(dirfd(d), de->d_name, 0) < 0)
+                                log_warning("Failed to remove /run/systemd/journal/streams/%s: %m",
+                                            de->d_name);
                         continue;
                 }
 

src/login/logind.c

@@ -323,7 +323,9 @@ static int manager_enumerate_seats(Manager *m) {
 
                 s = hashmap_get(m->seats, de->d_name);
                 if (!s) {
-                        unlinkat(dirfd(d), de->d_name, 0);
+                        if (unlinkat(dirfd(d), de->d_name, 0) < 0)
+                                log_warning("Failed to remove /run/systemd/seats/%s: %m",
+                                            de->d_name);
                         continue;
                 }
 

src/udev/udev-watch.c

@@ -79,7 +79,7 @@ void udev_watch_restore(struct udev *udev) {
                         udev_watch_begin(udev, dev);
                         udev_device_unref(dev);
 unlink:
-                        unlinkat(dirfd(dir), ent->d_name, 0);
+                        (void) unlinkat(dirfd(dir), ent->d_name, 0);
                 }
 
                 closedir(dir);