complibs/cloog: fix linking with libstdc++

This rules out 0.15.5 and previous versions, that did not
have this option, so remove them from the list. Anyway,
they were marked 'OBSOLETE', so it's not a big loss...

[Yann E. MORIN: remove obsolete versions]
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

 # Compute s390-specific values

 CT_DoArchTupleValues() {

     # That's the only thing to override

     if [ "${CT_ARCH_64}" = "y" ]; then

         CT_TARGET_ARCH="s390x"

     fi

 }