This runs in 100ms increments, so there's not a lot of harm in trying
longer - it should take the same time everywhere it succeeded before.
But I've reproduced failures on FreeBSD 13 on sr.ht, so there's at
least one platform where a total time of 1 second isn't enough.
Now we do 50 tries, which is 5 seconds.
When fish starts, it notices which pgroup owns the tty, and then it
restores that pgroup's tty ownership when it exits. However if fish does
not own the tty, then (on Mac at least) the tcsetpgrp call triggers a
SIGSTOP and fish will hang while trying to exit.
The first change is to ignore SIGTTOU instead of defaulting it. This
prevents the hang; however it risks re-introducing #7060.
The second change somewhat mitigates the risk of the first: only do the
restore if the initial pgroup is different than fish's pgroup. This
prevents some useless calls which might potentially steal the tty from
another process (e.g. in #7060).
