The issue with ISL has also been mentioned here: Pynq Compilation isl: download fail and here: Cannot build PYNQ2.7 because isl.gforge.inria site is shut down - #2 by bierkof
The issue with ISL has also been mentioned here: Pynq Compilation isl: download fail and here: Cannot build PYNQ2.7 because isl.gforge.inria site is shut down - #2 by bierkof