In addition to requiring nanosecond precision, using the native clock requires that the hardware TSC has a precision greater than the emulated CPU and its clock counter.
- Previous optimized impl. resulted in an integer overflow, so revert.
- This is our slow/fallback path that should never be really be used, so the optimization in unimportant.
From -fsanitize=address, this code wasn't calling the proper destructor.
Adding virtual destructors for each inherited class and the base class
fixes this bug.
While we are at it, mark the functions as final.
