Shut up a warning in cpu_clock_by_ic().

Namely, printing a uint64_t with printf(...%llu...) is considered bad
practice; you need to use the format specifier PRIu64, defined in
inttypes.h. Apparently, it's not safe to assume that
uint64_t == unsigned long long.

However, I don't like this kind of formatting uglyness.
The td variable on my machine is ~30k - and conceivably can't go
above 1M. Moreover, this printf is only for detailed debug purposes.
So it's safe to cast the var to int and print it with %d.