> From: Fabrice Popineau <fabrice.popineau@centralesupelec.fr>
> Date: Thu, 16 Nov 2017 17:31:40 +0100
> Cc: Phillip Lord <phillip.lord@russet.org.uk>,
>       Jostein Kjønigsen <jostein@kjonigsen.net>,
>       Jostein Kjønigsen <jostein@secure.kjonigsen.net>,
>       Drew Adams <drew.adams@oracle.com>, Emacs developers <emacs-devel@gnu.org>
>
>  > The last step takes an hour.
>
>  Try "make -j8" instead, and it will end much faster.
>
> Well, the slow part is still configure, because of the numerous instances of shell that are launched.

Not here, it isn't.  The slow part is byte compilation of the files
with bootstrap-emacs, until it is rebuilt with byte-compiled compiler.