tools/isl: update to 0.27

tools/isl: update to 0.27

version: 0.27
 date: Sun Sep  1 12:07:24 PM CEST 2024
 changes:
         - improved modulo detection
         - remove all unused local variables from affine expressions
         - minor improvements to coalescing
         - minor improvements to lexicographic optimization
         - improved constraint simplification
         - fix handling of empty piecewise expressions

Signed-off-by: Mieczyslaw Nalewaj <namiltd@yahoo.com>
Link: https://github.com/openwrt/openwrt/pull/18249
Signed-off-by: Nick Hainke <vincent@systemli.org>