Make "set debug frame 1" output print <not saved> instead of <optimized out>.

Make "set debug frame 1" output print <not saved> instead of <optimized out>.

"set debug frame 1" is printing "<optimized out>" for not saved
registers.  That's because the unwinders are returning optimized out
not_lval values instead of optimized out lval_register values.  "<not
saved>" is how val_print_optimized_out prints lval_register values.

  ...
  - { frame_unwind_register_value (frame=0,regnum=7(rsp),...) -> <optimized out> }
  + { frame_unwind_register_value (frame=0,regnum=7(rsp),...) -> <not saved> }
  ...

Tested on x86_64 Fedora 17.

2013-11-27  Pedro Alves  <palves@redhat.com>

	* frame-unwind.c (frame_unwind_got_optimized): Return
	an lval_register value instead of a not_lval value.