I had the same experience a couple of months ago. I spent a weekend banging my head against a wall following their documentation to cross-compile for pi3. Turns out it was out of date and there were also a couple of bugs. Since then they did fix one of the issues I reported. The other one already had a long open issue with no resolution (at the time). But I've lost all interest in trying again for the foreseeable future and I wouldn't recommend the experience.