isl_basic_map_insert: preserve emptiness
isl_basic_map_insert: preserve emptiness

isl_basic_map_plain_is_empty doesn't look at the constraints but only
at the ISL_BASIC_MAP_EMPTY flag.  We therefore need to make sure the
flag is set on the output of isl_basic_map_insert if it was set on the
input.

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

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