This fixes unwanted/incorrect cpu_affinity use on dead worker processes
respawn.  While this is not ideal, it's expected to be better when previous
situation where multiple processes were spawn with identical CPU affinity
set.

Reported by Charles Chen.

The only thing we could potentially do here in case of error
returned is to complain to error log, but we don't have log
structure available here due to interface limitations.

Prodded by Coverity.

HP-UX needs _HPUX_ALT_XOPEN_SOCKET_API to be defined to be able to
use various POSIX versions of networking functions.  Notably sendmsg()
resulted in "sendmsg() failed (9: Bad file number)" alerts without it.

See xopen_networking(7) for more details.

Poll event method needs ngx_cycle->files to work, and use of ngx_exit_cycle
without files set caused null pointer dereference in resolver's cleanup
on udp socket close.

After jemalloc 3.0.0 import there is no _malloc_options symbol, it has
been replaced with the malloc_conf one with a different syntax.

In case of EMFILE/ENFILE returned from accept() we disable accept events,
and (in case of no accept mutex used) arm timer to re-enable them later.
With accept mutex we just drop it, and rely on normal accept mutex handling
to re-enable accept events once it's acquired again.

As we now handle errors in question, logging level was changed to "crit"
(instead of "alert" used for unknown errors).

Note: the code might call ngx_enable_accept_events() multiple times if
there are many listen sockets.  The ngx_enable_accept_events() function was
modified to check if connection is already active (via c->read->active) and
skip it then, thus making multiple calls safe.