bug#44674: 28.0.50; Adding current-cpu-time for performance tests

[Stefan Monnier]

>> What do you mean by "origin" and by "calling 'system'"?
> Quoting https://pubs.opengroup.org/onlinepubs/9699919799/:
>
>           The clock() function shall return the implementation's best
>           approximation to the processor time used by the process
>           since the beginning of an implementation-defined era
>         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>         related only to the process invocation.
>
> How do you write portable Lisp code that returns consistent results
> based on such shaky foundations?

You only consider differences between measurements.


        Stefan