Attempting to compile filebeat in AIX

@arlequin @trex58 I am currently working on a PR to easily define feature at compile time, I believe that will help in your case, It's not ready yet.

We could have an include defined for your specific platform like AIX.

The following error message come from a dependency defined by our testing helpers, which seems to fallback to a windows

Have set the GOPATH and GOROOT correctly and I'm getting this error:
../vendor/github.com/fatih/color/color.go:21:12: error: reference to undefined identifier 'isatty.IsTerminal'
(!isatty.IsTerminal(os.Stdout.Fd()) && !isatty.IsCygwinTerminal(os.Stdout.Fd()))
[......]