bug#36649: 27.0.50; pure space and pdumper

[Robert Pluim]

>>>>> On Thu, 4 Mar 2021 12:55:34 +0000, Pip Cet <pipcet@gmail.com> said:

    Pip> On Wed, Mar 3, 2021 at 3:34 PM Pip Cet <pipcet@gmail.com> wrote:
    >> I have time for that now, so here's a revised patch as a first step.

    Pip> This patch removes pure space from Emacs 28.

Cool! Finally! Commit && push, damn the torpedoes.

    Pip> Changes:
    Pip> - now builds with --enable-checking=all

    Pip> Todo:
    Pip> - commit message not yet final.
    Pip> - zero vector handling depends on Qnil being all zero in memory

I think Emacs already assumes Qnil == 0, since there are places that
use ! to check for Qnil rather than using NILP.

Robert
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