Cross compile metricbeat for FreeBSD

Hi @Peek :slight_smile:

I've just done a full clean install in an Ubuntu Docker image without problem so we can discard a problem in the procedure.

I have realized that HugeTLBPages isn't supported in FreeBSD at the moment as you can see here https://github.com/elastic/gosigar

My only suggestion, right now, is to try to build it without the system and windows, which are the Metricbeat modules that uses gosigar but at the same time, libbeat library also uses it so I'm not sure if it will work.