5218 posix definition of NULL
correct unistd.h and iso/stddef_iso.h
update gate source affected

@@ -951,11 +951,11 @@
 
                                 len = strlen(func_strs[MODE]);
                                 if ((strncmp(str, func_strs[MODE], len) == 0) &&
                                     (*(str+(len)) == '=')) {
                                         for (str = (str+(++len)), i = 0;
-                                            *str != NULL; i++, str++) {
+                                            *str != '\0'; i++, str++) {
                                                 buf[i] = *str;
                                         }
                                 }
                                 buf[i] = '\0';
                                 DBG(2, ("buf_mode= %s\n", buf));