[PATCH] acinclude.m4: fix -std=c23 build failure

[Vincent Lefevre]

On 2025-01-21 10:33:34 +0000, Rudi Heitbaum wrote:
> Add prototype to configure test function as c23 removes unprototyped
> functions.
> 
> gcc-15 switched to -std=c23 by default:
> 
>     https://gcc.gnu.org/git/?p=gcc.git;a=commitdiff;h=55e3bd376b2214e200fa76d12b67ff259b06c212
> 
> As a result `configure` fails with:
>     conftest.c: In function 'f':
>     conftest.c:12:48: error: too many arguments to function 'g'; expected 0, have 6
>        12 | for(i=0;i<1;i++){if(e(got,got,9,d[i].n)==0)h();g(i,d[i].src,d[i].n,got,d[i].want,9);if(d[i].n)h();}}
>           |                                                ^ ~
>     conftest.c:7:6: note: declared here
>         7 | void g(){}
>           |      ^

Note that this was already reported.

> Link: https://gmplib.org/list-archives/gmp-bugs/2024-November/005550.html
> Signed-off-by: Rudi Heitbaum <rudi at heitbaum.com>
> ---
>  acinclude.m4 | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/acinclude.m4 b/acinclude.m4
> index fddb5fb07a..2d41de6328 100644
> --- a/acinclude.m4
> +++ b/acinclude.m4
> @@ -609,7 +609,7 @@ GMP_PROG_CC_WORKS_PART([$1], [long long reliability test 1],
>  
>  #if defined (__GNUC__) && ! defined (__cplusplus)
>  typedef unsigned long long t1;typedef t1*t2;
> -void g(){}
> +void g(...){}

Please don't. The (...) form is dirty and new, and not supported by
all compilers, e.g. even GCC 12:

tst2.c:1:8: error: ISO C requires a named argument before ‘...’
    1 | void g(...){}
      |        ^~~

The only good solution is to provide the prototype so that
type checking can be done.

-- 
Vincent Lefèvre <vincent at vinc17.net> - Web: <https://www.vinc17.net/>
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