add isl_int_gcdext
add isl_int_gcdext

We will use it in the next commit.

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

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