Merge pull request #2444 in SNORT/snort3 from ~MIALTIZE/snort3:freebsd to master

Merge pull request #2444 in SNORT/snort3 from ~MIALTIZE/snort3:freebsd to master

Squashed commit of the following:

commit c12beed04d5a2988dacc479a8c56b19fa1924412
Author: Michael Altizer <mialtize@cisco.com>
Date:   Mon Aug 31 22:58:40 2020 -0400

    helpers: Fix build on systems without sigaction

commit dc8959e04466d76792605447c3236fb2858f0104
Author: Michael Altizer <mialtize@cisco.com>
Date:   Mon Aug 31 22:53:15 2020 -0400

    helpers: Use sig_t instead of sighandler_t for better BSD compatibility