isl_map_union: avoid calling isl_map_union_disjoint
isl_map_union: avoid calling isl_map_union_disjoint

We will add a note to isl_map_union_disjoint in the next commit,
which does not apply to isl_map_union.

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

Meinersbur/isl,nicolasvasilache/isl,tobig/isl,nicolasvasilache/isl,VanirLLVM/toolchain_isl,BenzoSM/isl,jleben/isl,BenzoSM/isl,Distrotech/isl,PollyLabs/isl,SaberMod/isl-current,BenzoSM/isl,UBERTC/isl,BobSaget-Mod/libisl,inducer/isl-mirror,jleben/isl,Distrotech/isl,abduld/isl,crossbuild/isl,evaautomation/isl,PollyLabs/isl,BenzoSM/isl,Distrotech/isl,simbuerg/isl,KangDroidSMProject/ISL,crossbuild/isl,crossbuild/isl,UBERTC/isl,BobSaget-Mod/libisl,abduld/isl,SaberMod/isl-current,crossbuild/isl,jleben/isl,inducer/isl-mirror,jleben/isl,VanirLLVM/toolchain_isl,BenzoSM/isl,Meinersbur/isl,UBERTC/isl,PollyLabs/isl,KangDroidSMProject/ISL,simbuerg/isl,tobig/isl,tobig/isl,evaautomation/isl,Meinersbur/isl,SaberMod/isl-current,simbuerg/isl,inducer/isl-mirror,Meinersbur/isl,nicolasvasilache/isl,KangDroidSMProject/ISL,nicolasvasilache/isl,abduld/isl,BobSaget-Mod/libisl,PollyLabs/isl,VanirLLVM/toolchain_isl,nicolasvasilache/isl,evaautomation/isl,Distrotech/isl,simbuerg/isl,BobSaget-Mod/libisl,inducer/isl-mirror,inducer/isl-mirror,KangDroidSMProject/ISL,VanirLLVM/toolchain_isl,jleben/isl,SaberMod/isl-current,simbuerg/isl,Distrotech/isl,UBERTC/isl,BobSaget-Mod/libisl,KangDroidSMProject/ISL,abduld/isl,PollyLabs/isl,VanirLLVM/toolchain_isl,tobig/isl,evaautomation/isl