RTS uses suboptimal ticker implementation.

For posix-based hosts we have 3 implementations of the RTS ticket/timer. See https://gitlab.haskell.org/ghc/ghc/-/wikis/commentary/rts/signals#the-rts-timer-signal

Based on this wiki page/the source we want to use:

• Pthreat based one if we have timerfd support.
• TimerCreate(with Signals) otherwise if supported.
• setitimer based one otherwise (Again using signals)

We check for timerfd support via HAVE_SYS_TIMERFD_H. But it seems this is not set ever! It's certainly not set for my system, which has the appropriate header.
So we end up using the TimerCreate implementation instead.

I assume what is missing is a check for the header during configure. But maybe we should default to the pthread based implementation anyway, even if we don't have timerfd support.