ARM: Make the ARM native tracer stop M5 if control diverges.

ARM: Make the ARM native tracer stop M5 if control diverges.
If the control flow of M5's executable and statetrace's target process get out
of sync even a little, there will be a LOT of output, very little of which
will be useful. There's also almost no hope for recovery. In those cases, we
might as well give up and not generate a huge, mostly worthless trace file.