Update to isl-0.20-65-gb822a210

This update fixes https://https:/llvm.org/PR38348. Thanks Michael for
reporting the issue to isl and Sven for fixing the issue.

git-svn-id: https://llvm.org/svn/llvm-project/polly/trunk@339311 91177308-0d34-0410-b5e6-96231b3b80d8
22 files changed