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

[Eli Zaretskii]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Cc: mattiase@acm.org,  p.stephani2@gmail.com,  44674@debbugs.gnu.org
> Date: Mon, 16 Nov 2020 13:41:59 -0500
> 
> > Sorry, forgot to answer the 'system' part.  The issue there is whether
> > calling 'system' (and in general waiting for sub-processes to exit) is
> > counted against the process's use of CPU or not.  AFAIK, this is not
> > well defined, either.
> 
> Ah, I must admit that for the cases that interest me the distinction is
> of no consequence.  I don't even know which behavior I'd prefer.

Well, we are talking about a general-purpose API, so the semantics
should be well defined.  And for 'clock', it isn't.