Use of _res in multithreaded programs is problematical

Steps to reproduce:

Build zabbix 3.2.x, try to run it.
You end up with this entry in the zabbix_agentd.log file:

_res is not supported for multi-threaded programs.

and zabbix_agentd will abort(), via the "trap" NetBSD has
for this attempted usage in its pthread library.

See attached patch file...
The use of the new resolver interface should probably be
conditional on an autoconf test for whether it is available;
the supplied patch does not contain any machinery for that.