isl_pw_multi_aff_from_map: extract out pw_multi_aff_from_map_check_strides
isl_pw_multi_aff_from_map: extract out pw_multi_aff_from_map_check_strides

This reduces the size of isl_pw_multi_aff_from_map.

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

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