RFA: add debug hook to unwinder

[Richard Henderson]

Tom Tromey wrote:
> +/* This function is called during unwinding.  It is intended as a hook
> +   for a debugger to intercept exceptions.  CFA is the CFA of the
> +   target frame.  HANDLER is the PC to which control will be
> +   transferred.  */
> +static void
> +_Unwind_DebugHook (void *cfa __attribute__ ((__unused__)),
> +		   void *handler __attribute__ ((__unused__)))
> +{
> +  asm ("");
> +}

I think you should mark this function noinline for safety.
Otherwise some future version of the compiler could decide
to inline this and eliminate the _Unwind_DebugHook symbol
entirely.


r~