isl_arg_parse: reset all flags with same option name whenever a flag is set
isl_arg_parse: reset all flags with same option name whenever a flag is set

Otherwise, there is no way to turn off a flag that is set by default.

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

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