bug#42305: 28.0.50; Compilation warnings with mini-gmp

[Eli Zaretskii <eliz@gnu.org>]

The configuration with mini-gmp, when GMP is not installed, doesn't
compile cleanly.  First, compilation in lib/ emits this warning:

    CC       mini-gmp-gnulib.o
  mini-gmp-gnulib.c:28:10: warning: unknown option after ‘#pragma GCC diagnostic’ kind [-Wpragmas]
  # pragma GCC diagnostic ignored "-Wsuggest-attribute=malloc"

Next, compilation in src/ yields further warnings:

  data.c: In function ‘bignum_arith_driver’:
  data.c:2811:9: warning: assignment from incompatible pointer type [enabled by default]
     accum = &mpz[0];
	   ^
  data.c:2833:13: warning: assignment from incompatible pointer type [enabled by default]
	 accum = &mpz[0];
	       ^
  data.c: In function ‘Flogcount’:
  data.c:3147:11: warning: assignment from incompatible pointer type [enabled by default]
      nonneg = &mpz[0];
	     ^

  floatfns.c: In function ‘rescale_for_division’:
  floatfns.c:374:10: warning: assignment from incompatible pointer type [enabled by default]
	 pn = t;
	    ^
  floatfns.c:382:10: warning: assignment from incompatible pointer type [enabled by default]
	 pn = t;
	    ^

  timefns.c: In function ‘frac_to_double’:
  timefns.c:622:9: warning: assignment from incompatible pointer type [enabled by default]
	 d = &mpz[1];
	   ^
  timefns.c:630:9: warning: assignment from incompatible pointer type [enabled by default]
	 n = &mpz[0];
	   ^
  timefns.c: In function ‘lisp_to_timespec’:
  timefns.c:923:21: warning: initialization from incompatible pointer type [enabled by default]
     mpz_t const *qt = q;
		       ^
  timefns.c: In function ‘time_arith’:
  timefns.c:1151:10: warning: assignment from incompatible pointer type [enabled by default]
      hzmin = hzmin1;
	    ^
  timefns.c: In function ‘time_cmp’:
  timefns.c:1265:10: warning: assignment from incompatible pointer type [enabled by default]
	 za = &mpz[0];
	    ^
  timefns.c:1266:10: warning: assignment from incompatible pointer type [enabled by default]
	 zb = &mpz[1];
	    ^

This is using

eliz@fencepost:~/git/emacs/trunk$ gcc --version
gcc (Ubuntu 4.8.4-2ubuntu1~14.04.4) 4.8.4
Copyright (C) 2013 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.


In GNU Emacs 28.0.50 (build 20, x86_64-pc-linux-gnu, GTK+ Version 2.24.23, cairo version 1.13.1)
 of 2020-07-10 built on fencepost.gnu.org
Repository revision: 9ade7ea7b77ec40c16deb4dff139ce7127a703e2
Repository branch: master
System Description: Trisquel GNU/Linux Belenos (7.0)

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.

Configured using:
 'configure --with-gif=no --with-tiff=no --with-jpeg=no --with-modules

Configured features:
XPM PNG CAIRO SOUND GSETTINGS GLIB NOTIFY INOTIFY ACL LIBSELINUX GNUTLS
LIBXML2 FREETYPE HARFBUZZ M17N_FLT LIBOTF ZLIB TOOLKIT_SCROLL_BARS GTK2
X11 XDBE XIM MODULES THREADS PDUMPER

Important settings:
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  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
  font-lock-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: 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
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
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 term/xterm xterm byte-opt gv bytecomp
byte-compile cconv tooltip eldoc electric uniquify ediff-hook vc-hooks
lisp-float-type mwheel term/x-win x-win term/common-win x-dnd 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 inotify
dynamic-setting system-font-setting font-render-setting cairo
move-toolbar gtk x-toolkit x multi-tty make-network-process emacs)

Memory information:
((conses 16 47162 6676)
 (symbols 48 6045 1)
 (strings 32 15344 1830)
 (string-bytes 1 501765)
 (vectors 16 7245)
 (vector-slots 8 75540 8480)
 (floats 8 22 301)
 (intervals 56 181 0)
 (buffers 992 10)
 (heap 1024 3481 920))