pthreadpool: maintain a list of job_states on each pthreadpool_tevent_glue

pthreadpool: maintain a list of job_states on each pthreadpool_tevent_glue

We should avoid traversing a linked list within a thread without holding
a mutex!

Using a mutex would be very tricky as we'll likely deadlock with
the mutexes at the raw pthreadpool layer.

So we use somekind of spinlock using atomic_thread_fence in order to
protect the access to job->state->glue->{tctx,ev} in
pthreadpool_tevent_job_signal().

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>