Support for __builtin_thread_pointer / __builtin_set_thread_pointer:
        * config/arc/arc.md (arc_conditional_register_usage): Make
        arc_tp_regno a global rather than a fixed register.
        * config/arc/arc.md (get_thread_pointersi): New pattern.
        * config/arc/arc.md (set_thread_pointersi): Likewise.