Fix inline annotations in generated control-flow graphs for programs with multiple functions

[qmonnet]

The example provided by Christoph on the mailing list, for a separate issue, produces a graph with two functions:

On func_1(), on the right-hand side of the picture, we can observe that the inline annotations are not correct: they should be the annotations for the do_barf() function, but instead they duplicate the lines from handle__sched_process_exec().

There seems to be an issue in the way we print the line information for the control graph: we offset the annotation lines from the start of the program, not from the start of the function.