bug#41321: 27.0.91; Emacs aborts due to invalid pseudovector objects

[Eli Zaretskii]

> Cc: pipcet@gmail.com, 41321@debbugs.gnu.org, monnier@iro.umontreal.ca
> From: Paul Eggert <eggert@cs.ucla.edu>
> Date: Tue, 26 May 2020 15:49:24 -0700
> 
> > On non-USE_LSB_TAG systems, GCALIGNMENT is 1, so this doesn't look
> > right (or maybe I'm missing something).
> 
> Good point; I'd neglected that. I.e., on !USE_LSB_TAG systems the proposed
> emacs-27 patch is overly-conservative, as it causes maybe_lisp_pointer to 
> always
> return true. Although this hurts GC performance it doesn't affect correctness
> and the patch does fix a crash on USE_LSB_TAG systems, so it (or something 
> like
> it) is needed for emacs-27.

We used to rely on 8-byte alignment on those systems, and I don't see
any reason not to continue relying on that and punishing those
systems' performance.  What would we gain?