New "make benchmark" target

[Stefan Kangas]

Pip Cet via "Emacs development discussions." <emacs-devel@gnu.org>
writes:

> https://elpa.gnu.org/packages/elisp-benchmarks.html ? It'd be great if
> we could agree on a benchmark, and even better if there were a way to
> reliably run it from emacs -Q :-)
>
> In fact, I would suggest to move a reduced benchmark suite to the emacs
> repo itself, and run it using "make benchmark".

SGTM, but why a reduced suite and not just the whole thing?