[#2269] Update support for solaris.

Problem
======

Support for solaris was interrupted a few releases ago and we want to re-enable it.

Changes
=======

Update testing support for solaris.

Only a single FS function required update for solaris.

From now on, all compat builds will require to pass on solaris

How to test
=========

reviewers: @alibotean 

check that changes make sense.


Thanks!