isl_tab_pip.c: isl_sol: keep track of space of output
isl_tab_pip.c: isl_sol: keep track of space of output

This will be useful when the internal representation of partial
solutions is changed from an isl_mat to an isl_multi_aff
in the next commit.

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

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