[gprof] disjoint histograms

[Ben Elliston]

> > The attached patch makes gprof support histogram records
> > will different memory ranges, provided those memory ranges
> > never overlap. This is done by adding new structure, 'struct histogram'
> > adding a linked list of such structures and modifying gprof to use this
> > linked list.
> 
> Did anyone have comments on this patch, or objections?  Otherwise,
> I'll review it myself in a few days.

The reasoning is sound.  I haven't looked at the patch closely, though.

Ben