PR/48559 lwp park compat

[christos%zoulas.com@localhost (Christos Zoulas)]

Hi,

Last March we discovered an issue with pthread_cond_timedwait()
and specifying different clocks (CLOCK_MONOTONIC vs CLOCK_REALTIME).
While this was fixed in libpthread, the proper fix would be to do
it in the kernel in _lwp_park(2).  This was done, but the kernel
syscall was not exported to userland allowing us to remove this
hack because people wanted more time to explore other changes
to _lwp_park(2) that might also change the footprint of the syscall.

Well, this has not happened, so I am proposing to export the existing
new ABI to userland so that libpthread can use it and stops using the
compat call.

I will do so on Friday if I don't hear otherwise.

christos