Update isl to include
https://repo.or.cz/isl.git/commit/fc484e004200964f8f18249de1f510393ec924a9
which fixes#180000.
The isl update also fixes#34710 which had the same cause but with an
empty access domain (#180000 has an empty statement domain). Thus we
also revert 163cacb46960be4dd0d8562737bbf0ea97cb14ad which now only adds
unnecessary overhead.
A regression test has been added to isl which is why we do not add a
test in Polly.
Fixes: #180000
Thanks @skimo-openhub for the fix and @thapgua for the bugreport.
ac57c4a728