isl_scheduler.c: compute_schedule_wcc: extract out compute_schedule_finish_band
isl_scheduler.c: compute_schedule_wcc: extract out compute_schedule_finish_band

This reduces the size of compute_schedule_wcc and, together with
the next commit, this will allow us to perform additional computations
between the pure construction of a band and the incoporation of
that band in the schedule.  This will allow us in particular
to attempt to combine strongly connected components first.

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

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