ira.c (struct equivalence): Promote INIT_INSNs field to an rtx_insn_list.

ira.c (struct equivalence): Promote INIT_INSNs field to an rtx_insn_list.

        * ira.c (struct equivalence): Promote INIT_INSNs field to
        an rtx_insn_list.  Add comments.
        (no_equiv): Promote LIST to an rtx_insn_list.  Update
        testing for and creating the special marker.  Use methods
        to extract the insn and next pointers.  Promote INSN to an
        rtx_insn.
        (update_equiv_regs): Update test for special marker in the
        INIT_INSNs list.

From-SVN: r216095