allow isl_ids with negative reference counts
allow isl_ids with negative reference counts

This will be useful for static isl_ids that are not supposed to change.

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

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