it's not putty, seems that you are trying gdb on an device that it cpu arch wont support by gdb (should be arm64). Use lldb instead.
U can see this in Apple's code
switch (info.osabi)
{
case GDB_OSABI_DARWIN:
info.bfd_arch_info = bfd_lookup_arch (bfd_arch_arm, 0);
break;
case GDB_OSABI_DARWINV6:
info.bfd_arch_info = bfd_lookup_arch (bfd_arch_arm, bfd_mach_arm_6);
break;
case GDB_OSABI_DARWINV7:
info.bfd_arch_info = bfd_lookup_arch (bfd_arch_arm, bfd_mach_arm_7);
break;
case GDB_OSABI_DARWINV7F:
info.bfd_arch_info = bfd_lookup_arch (bfd_arch_arm, bfd_mach_arm_7f);
break;
case GDB_OSABI_DARWINV7K:
info.bfd_arch_info = bfd_lookup_arch (bfd_arch_arm, bfd_mach_arm_7k);
break;
default:
warning ("Unrecognized osabi %d in arm_set_osabi_from_host_info", (int) info.osabi);
}