vm: Better idea: Directly copy flags.
vm: Better idea: Directly copy flags.

Now that SYM_SCOPE_GLOBAL is no longer being inserted into register flags, the
register flags can be copied using plain old assignments. Right now, the only
flag set on a register is SYM_IS_NIL.

crasm/lily,crasm/lily,boardwalk/lily,boardwalk/lily,crasm/lily