* frame.c (set_unwind_by_pc): Use dummy_frame_register_unwind.
* dummy-frame.c (find_dummy_frame): Rename
generic_find_dummy_frame, make static. Return the dummy frame
instead of the regcache.
(generic_find_dummy_frame): Re-implement using find_dummy_frame,
(cached_find_dummy_frame): New function. Use find_dummy_frame.
(dummy_frame_register_unwind): Rename
generic_call_dummy_register_unwind. Use cached_find_dummy_frame.
* dummy-frame.h (dummy_frame_register_unwind): Rename
generic_call_dummy_register_unwind.