Update isl to isl-0.18-1047-g4a20ef8
- Removes several deprecated functions (e.g., isl_band).
- Improves the pretty-printing of sets by detecting modulos and "false" equalities.
- Minor improvements to coalescing and increased robustness of the isl scheduler.
This update does not yet include isl commit isl-0.18-90-gd00cb45
(isl_pw_*_alloc: add missing check for compatible spaces, Wed Sep 6 12:18:04
2017 +0200), as this additional check is too tight and unfortunately causes
two test case failures in Polly. A patch has been submitted to isl and will be
included in the next isl update for Polly.