Update isl to isl-0.24-69-g54aac5ac

This is needed for having the functions isl_{set,map}_n_basic_{set,map}
exported to the C++ interface.
Some tests have been modified to reflect the isl changes.

GitOrigin-RevId: ec3da1a43f1f0fe706e7ea511ab66a3e1dd0a2f2
23 files changed