Thanks, TheOuch! I did read this trick in the README, but wasn't sure whether that would fix it, or maybe cause more problems. My X-server was working (without 3D-acceleration), so I didn't want to mess up that.
After reading your reply, I went through the README again, and found this:
# cat /proc/version
# gcc -v
Since the output of those two showed the same compiler, I trusted you were right, and you were.......till now. But in difference to another major OS, my experience with Linux is; what works, stays working !!
What else can I say (to myself and other impatient fellows)? READ THE F****** MANUAL !
By the way; with sax2 you don't have to edit the XF86Config file (sax2 takes care of that).
All in all simply a rather harmless bug in the installer(?).