Fix implicit declaration errors.

--- configure.orig	2015-04-24 13:54:36
+++ configure	2025-09-11 11:43:14
@@ -5065,14 +5065,14 @@
 
 #define XOR(e, f) (((e) && !(f)) || (!(e) && (f)))
 int
-main ()
+main (void)
 {
   int i;
   for (i = 0; i < 256; i++)
     if (XOR (islower (i), ISLOWER (i))
 	|| toupper (i) != TOUPPER (i))
-      exit(2);
-  exit (0);
+      return (2);
+  return (0);
 }
 _ACEOF
 rm -f conftest$ac_exeext
@@ -19498,14 +19498,14 @@
 
 #define XOR(e, f) (((e) && !(f)) || (!(e) && (f)))
 int
-main ()
+main (void)
 {
   int i;
   for (i = 0; i < 256; i++)
     if (XOR (islower (i), ISLOWER (i))
 	|| toupper (i) != TOUPPER (i))
-      exit(2);
-  exit (0);
+      return (2);
+  return (0);
 }
 _ACEOF
 rm -f conftest$ac_exeext