isl_stream_read_map: add partial support for reading rational sets
isl_stream_read_map: add partial support for reading rational sets

The support is incomplete, but enough to read the inputs in the test
cases of the next commit.

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

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