src/long-options.c: Fix prototype of parse_long_options for GCC 15

Symptom was:
> long-options.c:51:1: error: conflicting types for 'parse_long_options'; have 'void(int,  char **, const char *, const char *, const char *, const char *, void (*)(void))'
>    51 | parse_long_options (int argc,
>       | ^~~~~~~~~~~~~~~~~~
> In file included from long-options.c:30:
> long-options.h:29:3: note: previous declaration of 'parse_long_options' with type 'void(int,  char **, const char *, const char *, const char *, const char *, void (*)(int))'
>    29 |   parse_long_options PARAMS ((int _argc,
>       |   ^~~~~~~~~~~~~~~~~~
> long-options.c: In function 'parse_long_options':
> long-options.c:73:12: error: too many arguments to function 'usage_func'
>    73 |           (*usage_func) (0);
>       |           ~^~~~~~~~~~~~

Author: hartwork

src/long-options.c

@@ -54,7 +54,7 @@ parse_long_options (int argc,
 		    const char *package,
 		    const char *version,
 		    const char *authors,
-		    void (*usage_func)())
+		    void (*usage_func)(int))
 {
   int c;
   int saved_opterr;