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

[Eli Zaretskii <eliz@gnu.org>]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: 42305@debbugs.gnu.org
> Date: Sat, 17 Oct 2020 12:04:05 +0200
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > 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"
> 
> Is this with
> 
> ./configure --without-libgmp

No, this is on a system without GMP.  config.log says:

  configure:18948: checking gmp.h usability
  configure:18948: gcc -std=gnu11 -c  -O0 -g3     conftest.c >&5
  configure:18948: $? = 0
  configure:18948: result: yes
  configure:18948: checking gmp.h presence
  configure:18948: gcc -std=gnu11 -E     conftest.c
  configure:18948: $? = 0
  configure:18948: result: yes
  configure:18948: checking for gmp.h
  configure:18948: result: yes
  configure:18954: checking for library containing __gmpz_roinit_n
  configure:18985: gcc -std=gnu11 -o conftest  -O0 -g3       conftest.c -lX11   >&5
  /tmp/cchXnJLF.o: In function `main':
  /home/e/eliz/git/emacs/branch/conftest.c:221: undefined reference to `__gmpz_roinit_n'
  collect2: error: ld returned 1 exit status
  configure:18985: $? = 1
  ...
  configure:19002: result: no

The results should be identical, though, AFAIU.

> If so, I'm not able to reproduce the bug on Debian bullseye.

With what version of GCC?  This could be dependent on the compiler
version; mine in that case is

  gcc (Ubuntu 4.8.4-2ubuntu1~14.04.4) 4.8.4

as was reported originally.  (This is on fencepost.gnu.org, btw.)

> But I see that mini-gmp-gnulib.c was updated a couple of weeks after
> you reported this.  Are you still seeing these warnings on your
> system?

The warning in mini-gmp-gnulib.c is indeed gone, but GMP-related
warnings in our own sources still remain.  Examples:

  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;
	    ^
    CC       fns.o
  data.c: In function ‘bignum_arith_driver’:
  data.c:2821:9: warning: assignment from incompatible pointer type [enabled by default]
     accum = &mpz[0];
	   ^
  data.c:2843:13: warning: assignment from incompatible pointer type [enabled by default]
	 accum = &mpz[0];
	       ^
  data.c: In function ‘Flogcount’:
  data.c:3157:11: warning: assignment from incompatible pointer type [enabled by default]
      nonneg = &mpz[0];
	     ^
    CC       emacs-module.o
    CC       timefns.o
  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];
	    ^