bug#50453: 27.2; Portable dumper broken on MSW

[Po Lu]

Having recently had an opportunity to update the Emacs installed on some
machines previously running 24.5, I noticed that Emacs 27.2 doesn't seem
to load portable dumps, and instead fails with an out-of-memory error,
the precise error message being:

emacs: could not load dump file
"C:\PROGRAM FILES\EMACS\I686\libexec/emacs/27.2/i686-w64-mingw32/emacs.pdmp": 
out of memory.

Emacs operates normally if the portable dump file is removed, or when
using unexec dumping.

Admittedly, the machine is a Pentium 4 with 768 megabytes of memory (and
what would you expect from a PC used to operate legacy software), but I
see no reason loading pdumps should require more than that, as the
previous dumper worked just fine.

In GNU Emacs 27.2 (build 1, i686-w64-mingw32)
 of 2021-09-07 built on bubbles
Windowing system distributor 'Microsoft Corp.', version 4.10.2222
System Description: Microsoft Windows 98 (v4.10.2222)

Recent messages:

Configured using:
 'configure --without-dbus --host=i686-w64-mingw32
 --without-compress-install 'CFLAGS=-O2 -static''

Configured features:
XPM JPEG TIFF GIF PNG RSVG SOUND NOTIFY W32NOTIFY ACL GNUTLS LIBXML2
HARFBUZZ ZLIB TOOLKIT_SCROLL_BARS MODULES THREADS JSON PDUMPER LCMS2 GMP

Important settings:
  value of $LANG: enu
  locale-coding-system: cp1252

Major mode: Fundamental

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  buffer-read-only: t
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message rmc puny dired dired-loaddefs
format-spec rfc822 mml easymenu mml-sec password-cache epa derived epg
epg-config gnus-util rmail rmail-loaddefs text-property-search time-date
subr-x seq byte-opt gv bytecomp byte-compile cconv mm-decode mm-bodies
mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader cl-loaddefs
cl-lib sendmail rfc2047 rfc2045 ietf-drums mm-util mail-prsvr mail-utils
warnings tooltip cus-start eldoc electric uniquify ediff-hook vc-hooks
lisp-float-type mwheel dos-w32 ls-lisp disp-table term/w32-win w32-win
w32-vars term/common-win tool-bar dnd fontset image regexp-opt fringe
tabulated-list replace newcomment text-mode elisp-mode lisp-mode
prog-mode register page tab-bar menu-bar rfn-eshadow isearch timer
select scroll-bar mouse jit-lock font-lock syntax facemenu font-core
term/tty-colors frame minibuffer cl-generic cham georgian utf-8-lang
misc-lang vietnamese tibetan thai tai-viet lao korean japanese eucjp-ms
cp51932 hebrew greek romanian slovak czech european ethiopic indian
cyrillic chinese composite charscript charprop case-table epa-hook
jka-cmpr-hook help simple abbrev obarray cl-preloaded nadvice loaddefs
button faces cus-face macroexp files text-properties overlay sha1 md5
base64 format env code-pages mule custom widget hashtable-print-readable
backquote threads w32notify w32 lcms2 multi-tty make-network-process
emacs)

Memory information:
((conses 8 163155 11505)
 (symbols 24 20691 1)
 (strings 16 56914 2810)
 (string-bytes 1 2369595)
 (vectors 8 30187)
 (vector-slots 4 1194144 19878)
 (floats 8 199 93)
 (intervals 28 286 32)
 (buffers 576 13))