isl_basic_map_remove_unknown_divs: restart whenever div has been removed
isl_basic_map_remove_unknown_divs: restart whenever div has been removed

The call to isl_basic_map_remove_dims may end up calling
isl_basic_map_simplify, which may in turn remove additional divs
if they no longer occur in any constraint.

Signed-off-by: Sven Verdoolaege <e5350bbed4977f5eb8ae1dc6abd9ae59d21ace75@kotnet.org>

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