curious gprof behaviour on trivial testcase

[Ben Elliston]

Hi Jim

> The problem here is that a trivial testcase has only one function,
> and hence no call graph info.  However, gprof by default assumes you
> want to emit call graph info, and if there is none, it gives an
> error.

Thanks for fixing this -- it caught me recently and I didn't get a
chance to go back and try to fix it myself.

More to the point, the error message you get from gprof is utterly
unhelpful.  When I encountered it, I immediately suspected corruption
in the gmon.out file or operator error.  It had me scratching my head
for a bit!

Cheers, Ben