reg-stack.c (subst_stack_regs): Pop the stack register for a computed goto which sets the same stack register.

        * reg-stack.c (subst_stack_regs): Pop the stack register for a
        computed goto which sets the same stack register.

        * reg-stack.c (compare_for_stack_reg): Swap only if the source and
        destination are both on the regstack.
        (subst_stack_regs_pat): Put the destination at the top of the regstack.
Bring over regstack bugfixes from the FSF.

From-SVN: r15096