bug#43269: 28.0.50; [feature/native-comp] provide a user feedback on Emacs being native compiled

[Eli Zaretskii <eliz@gnu.org>]

> From: Richard Stallman <rms@gnu.org>
> Cc: akrl@sdf.org, arthur.miller@live.com, 43269@debbugs.gnu.org
> Date: Tue, 08 Sep 2020 23:45:06 -0400
> 
>   > As mentioned on the bug list, I'd prefer if user could defer native
>   > compilation to some later time, so as to avoid making the Emacs build
>   > take hours, especially on slow and low-end machines.
> 
> I wonder if I would ever see any benefit form the speedup of native
> compilation.  I hardly ever notice waiting for Emacs to do computation.
> But I would find a big slowdown in building to be a pain.
> 
> Maybe I would prefer to turn off native compilation, pure and simple.

I share some of these feelings, FWIW.  Andrea's work is, of course,
commendable and the results will be very welcome when they land on
master, but I'm disappointed by the high price we need to pay for this
feature, both in complexity (notice the long discussions of where and
how to store the *.eln files, and how to handle recompilation and
reloading), and in compilation times.  Having the single-core
compilation times increase from 10-15 min to several hours is
... extreme.  (And before you say no one runs this on a single core: I
sometimes do, when parallel builds get in the way of debugging some
problem.)  And we will probably bump into additional issues down the
road.

(How come it's so easy and seamless in Guile?)