It links neither in BLITZ nor in non-BLITZ mode. But when I switched Link mode to "Use shared libs", it linked properly. So it looks like a bug in the U++ make process which passes a wrong linker option (-lgtk-x11-2.0) or breaks the ld syntax when performing all-static linking.
If I remind, for some reason in linux you can use only shared libs mode. Only in windows you can switch to all static.