isl_union_*_alloc: project space onto parameters
isl_union_*_alloc: project space onto parameters

Before, we were expecting the user to provide a parameter space,
but we might as well project whatever the user gives us onto
its parameter space.

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

crossbuild/isl,epowers/isl,Meinersbur/isl,jleben/isl,crossbuild/isl,nicolasvasilache/isl,KangDroidSMProject/ISL,abduld/isl,inducer/isl-mirror,KangDroidSMProject/ISL,Distrotech/isl,crossbuild/isl,KangDroidSMProject/ISL,jleben/isl,tobig/isl,jleben/isl,epowers/isl,serge-sans-paille/isl,evaautomation/isl,simbuerg/isl,simbuerg/isl,Meinersbur/isl,epowers/isl,inducer/isl-mirror,BobSaget-Mod/libisl,SaberMod/isl-current,BobSaget-Mod/libisl,evaautomation/isl,BobSaget-Mod/libisl,abduld/isl,serge-sans-paille/isl,crossbuild/isl,nicolasvasilache/isl,Meinersbur/isl,SaberMod/isl-current,simbuerg/isl,UBERTC/isl,KangDroidSMProject/ISL,pierrotdelalune/isl,pierrotdelalune/isl,Distrotech/isl,PollyLabs/isl,serge-sans-paille/isl,abduld/isl,PollyLabs/isl,pierrotdelalune/isl,nicolasvasilache/isl,BenzoSM/isl,inducer/isl-mirror,Distrotech/isl,jleben/isl,VanirLLVM/toolchain_isl,BenzoSM/isl,simbuerg/isl,BobSaget-Mod/libisl,VanirLLVM/toolchain_isl,SaberMod/isl-current,cfx-next/toolchain_isl-upstream,cfx-next/toolchain_isl-upstream,epowers/isl,cfx-next/toolchain_isl-upstream,BenzoSM/isl,tobig/isl,BobSaget-Mod/libisl,VanirLLVM/toolchain_isl,cfx-next/toolchain_isl-upstream,UBERTC/isl,tobig/isl,SaberMod/isl-current,Distrotech/isl,KangDroidSMProject/ISL,simbuerg/isl,UBERTC/isl,epowers/isl,nicolasvasilache/isl,jleben/isl,VanirLLVM/toolchain_isl,tobig/isl,Meinersbur/isl,nicolasvasilache/isl,evaautomation/isl,BenzoSM/isl,pierrotdelalune/isl,inducer/isl-mirror,PollyLabs/isl,abduld/isl,UBERTC/isl,BenzoSM/isl,PollyLabs/isl,serge-sans-paille/isl,inducer/isl-mirror,Distrotech/isl,serge-sans-paille/isl,evaautomation/isl,pierrotdelalune/isl,PollyLabs/isl,VanirLLVM/toolchain_isl,cfx-next/toolchain_isl-upstream