bug#50453: 27.2; Portable dumper broken on MSW

[Eli Zaretskii]

> From: Po Lu <luangruo@yahoo.com>
> Cc: 50453@debbugs.gnu.org
> Date: Thu, 09 Sep 2021 20:55:02 +0800
> 
> If VM_SUPPORTED is defined to 0, Emacs loads the pdmp file normally.
> Perhaps Emacs could test for is_window_9x (), and if affirmative, fall
> back to using dump_mmap_contiguous_heap?

It's possible, but only as the last resort, because it will cause the
startup to be much slower.

How did you try that?  Did you rebuild Emacs?  If so, I would like you
to try a different change first, before we decide to give up on the
memory-mapped file approach.