comp-libs/cloog: fix building

For CLooG/PPL 0.15.3, the directory name was simply cloog-ppl.
For any later versions, the driectory name does have the version, such as
cloog-ppl-0.15.4.

 reporter_name="Matthias KAEHLCKE"

 reporter_url="http://sourceware.org/ml/crossgcc/2008-08/msg00055.html"

 reporter_comment=""