[RFA] Update PC values for JVMTI stack tracing code

[Kyle Galloway]

Tom Tromey wrote:
> Kyle> +    // If the pc is NULL, we are not debugging, so return something other than
> Kyle> +    // NULL.
> Kyle> +    if (pc_ptr == NULL)
> Kyle> +      pc = 0;
>
> This comment is pretty confusing since '0' is more or less a synonym
> for NULL.  The comment says we return something other than NULL but
> then we go ahead and do it anyway -- weird.
>
> How about just "If PC_PTR is NULL, we are not debugging"?
> I capitalized PC_PTR here to refer to its value; this is a GNU
> standard for "meta-syntactic variables", it is in the coding standards
> somewhere.
>
> Ok with that change.
>   
Seems logical.  I've made that change and checked this in.

Thanks,

Kyle