Some Linux syscalls - sigtimedwait(2), ppoll(2) and the like - should
not be restarted, even if the current signal mask specifies SA_RESTART.
See https://man7.org/linux/man-pages/man7/signal.7.html for details.
Because this has potential to break things, there's a new chicken flag,
compat.linux.ignore_erestart.
This should include poll(2), but it's a bit more involved and I'm not sure
if our poll(2) can actually return ERESTART?