build: add NetBSD support to opensslconf.h
build: add NetBSD support to opensslconf.h

Simplify the BSD list by defining OPENSSL_BSD if using a matching
BSD platform.
Add NetBSD to the list and update documentation.

PR-URL: #14313
Reviewed-By: Ben Noordhuis <59bd0a3ff43b32849b319e645d4798d8a5d1e889@bnoordhuis.nl>
Reviewed-By: James M Snell <2d64a127ffc94dbe6295928a16bedf8b26814159@gmail.com>

nodegit/nodegit,nodegit/nodegit,nodegit/nodegit,nodegit/nodegit,jmurzy/nodegit,jmurzy/nodegit,jmurzy/nodegit,nodegit/nodegit,jmurzy/nodegit,jmurzy/nodegit