I have no idea what would be causing the build failures at this point. Obviously everything works on Debian, so I can't reproduce the FTBFS and debug it here.
Well, we've been down this road before where things work in Debian and don't work in Slackware. :) And as we saw only a few days ago, I could well have something configured that is causing the builds to gag.
I would make sure that TQT_REAL_TQT is always set for each compiled file, as the build will fail in the manner shown if TQT_REAL_TQT is not set.
You're skipping some steps here. :) Make sure TQT_REAL_TQT is set where? Where and how do I check?
Darrell