OpenBSD: only get active CPU core count
OpenBSD: only get active CPU core count

Newer computers may have some cores offline because of the
Meltdown/Spectre patches from a while ago, making uv_cpu_info
potentially misleading and leading to people attempting to use more
threads than they actually have available. This makes it so only the
cores that are online and doing any work are counted.

PR-URL: https://github.com/libuv/libuv/pull/2326
Reviewed-By: Ben Noordhuis <59bd0a3ff43b32849b319e645d4798d8a5d1e889@bnoordhuis.nl>
Reviewed-By: Santiago Gimeno <3f17e29e343c4cf8809fb0970d81d6d8ee88d6b3@gmail.com>
Reviewed-By: Saúl Ibarra Corretgé <8a7991f6950ea189abf159d6ec98d2fcc13dc5f6@gmail.com>
Reviewed-By: Colin Ihrig <838f779c91673db29b8572ea3f54d191d3878ae2@gmail.com>

unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso