isl_map_simplify.c: extract out constraint_index_is_redundant
isl_map_simplify.c: extract out constraint_index_is_redundant

This function will be reused for checking the redundancy of inequalities
stored in a matrix.

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

BenzoSM/isl,tobig/isl,nicolasvasilache/isl,BenzoSM/isl,Meinersbur/isl,BenzoSM/isl,Meinersbur/isl,Meinersbur/isl,Meinersbur/isl,UBERTC/isl,inducer/isl-mirror,tobig/isl,Distrotech/isl,PollyLabs/isl,PollyLabs/isl,nicolasvasilache/isl,UBERTC/isl,UBERTC/isl,BenzoSM/isl,nicolasvasilache/isl,Distrotech/isl,inducer/isl-mirror,inducer/isl-mirror,Distrotech/isl,nicolasvasilache/isl,Distrotech/isl,nicolasvasilache/isl,Distrotech/isl,inducer/isl-mirror,PollyLabs/isl,UBERTC/isl,inducer/isl-mirror,PollyLabs/isl,tobig/isl,BenzoSM/isl,PollyLabs/isl,tobig/isl