build: fix warnings (shown on IRIX)

Appearing on IRIX with gcc -mabi=n32.
Reported by Bruno Haible.
https://lists.gnu.org/r/bug-bison/2020-05/msg00039.html

* examples/c++/variant-11.yy, examples/c/bistromathic/parse.y: Don't
give chars to isdigit, cast them to unsigned char before.
* src/complain.c: Use c_isdigit.
* src/fixits.c (fixits_run): Avoid casts.
* src/lalr.c (goto_print): Use %zu for a size_t.

examples/c++/variant-11.yy

@@ -139,7 +139,7 @@ namespace yy
 int
 main (int argc, const char *argv[])
 {
-  if (2 <= argc && isdigit (*argv[1]))
+  if (2 <= argc && isdigit (static_cast<unsigned char> (*argv[1])))
     {
       auto maxl = strtol (argv[1], nullptr, 10);
       max = INT_MIN <= maxl && maxl <= INT_MAX ? int(maxl) : 4;

examples/c/bistromathic/parse.y

@@ -363,7 +363,7 @@ yyreport_syntax_error (const yypcontext_t *ctx)
       }
     // %0e, %1e...: expected token.
     else if (format[0] == '%'
-             && isdigit (format[1])
+             && isdigit ((unsigned char) format[1])
              && format[2] == 'e'
              && (format[1] - '0') < argsize)
       {

src/complain.c

@@ -23,7 +23,7 @@
 #include "system.h"
 
 #include <argmatch.h>
-#include <ctype.h>
+#include <c-ctype.h>
 #include <progname.h>
 #include <stdarg.h>
 #include <sys/stat.h>
@@ -609,7 +609,7 @@ syntax_error (location loc,
 
   while (*format)
     if (format[0] == '%'
-        && isdigit (format[1])
+        && c_isdigit (format[1])
         && format[2] == '$'
         && format[3] == 's'
         && (format[1] - '0') < argc)

src/fixits.c

@@ -124,10 +124,11 @@ fixits_run (void)
   FILE *out = xfopen (input, "w");
   size_t line = 1;
   size_t offset = 1;
-  fixit const *f = NULL;
+  void const *p = NULL;
   gl_list_iterator_t iter = gl_list_iterator (fixits);
-  while (gl_list_iterator_next (&iter, (const void**) &f, NULL))
+  while (gl_list_iterator_next (&iter, &p, NULL))
     {
+      fixit const *f = p;
       /* Look for the correct line. */
       while (line < f->location.start.line)
         {

src/lalr.c

@@ -92,7 +92,7 @@ goto_print (goto_number i, FILE *out)
   const state_number dst = to_state[i];
   symbol_number var = states[dst]->accessing_symbol;
   fprintf (out,
-           "goto[%ld] = (%d, %s, %d)", i, src, symbols[var]->tag, dst);
+           "goto[%zu] = (%d, %s, %d)", i, src, symbols[var]->tag, dst);
 }
 
 void