lib/isl: The sources' hosting is down

[ajelinski]

The libisl package is failing because the package with sources is unavailable: http://isl.gforge.inria.fr/isl-0.21.tar.bz2.
In fact, this whole official isl hosting is down.

[ajelinski]

I'll skip the job building isl since we have that package on Anaconda already.
It won't be a real issue unless there are any problems with currently available packages or newer isl is needed.
Perhaps the official hosting will become available prior to that.