timers-urgent-2023-02-19

 Posix-timers armed with a short interval with an ignored signal result
 in an unpriviledged DoS. Due to the ignored signal the timer switches
 into self rearm mode. This issue had been "fixed" before but a rework of
 the alarmtimer code 5 years ago lost that workaround.

 There is no real good solution for this issue, which is also worked around
 in the core posix-timer code in the same way, but it certainly moved way
 up on the ever growing todo list.