Use a (signed) int32_t counter instead of an `unsigned int' counter
for the GPROF4 case. This allows a simpler method to be used for
non-statistical profiling (it allows overhead adjustments to be
subtracted from one counter without harm if that counter goes
negative; otherwise the adjustment would have to be distributed).

32 bit counters were already too small for GPROF4 with a 200MHz
clock. int64_t counters should be used.