1:1 Userland threading stage 4.4/4:

1:1 Userland threading stage 4.4/4:

Implement killlwps() and flesh out lwp_exit().  Lwps which have set the
LWP_WEXIT flag will terminate themselves by calling lwp_exit() from
userret().

Reap lwps in a per-CPU taskqueue.  NOTE: Even the last lwp of an exiting
proc will be reaped by the task queue, effectively leaving a BARE proc
to reap in wait4().

In-collaboration-with: Thomas E. Spanjaard <tgen@netphreax.net>