It seems that there is a race condition in the implementation of the
nx-x11 makefiles somewhere. On machines with many cores and high levels
of parallel workers (for me, 32 cores and -j20), nxcompext gets built
before libNX_X11 is ready:

+ ln -s ../../lib/X11/libNX_X11.so .
/usr/bin/ld: cannot find -lNX_X11
collect2: error: ld returned 1 exit status
make[9]: *** [libXcompext.so.3.5.0] Fehler 1
make[9]: Leaving directory `/srv/scratch/tartler/nx-libs/nxcompext'

Until those makefiles get fixed, better disable parallel operation