Additional fix to get Webalizer to compile under GCC 10. Untested - what does this program even do?
Index: webalizer-2.23-08/output.c
===================================================================
--- webalizer-2.23-08.orig/output.c
+++ webalizer-2.23-08/output.c
@@ -65,6 +65,9 @@
 #include "graphs.h"
 #include "output.h"
 
+extern struct response_url * respnotfound;
+extern struct responsetmp_url * respnotfoundtmp;
+extern u_long resp_counter;                               /* total 404 counter     */
 /* internal function prototypes */
 void    write_html_head(char *, FILE *);            /* head of html page   */
 void    write_html_tail(FILE *);                    /* tail of html page   */
Index: webalizer-2.23-08/preserve.c
===================================================================
--- webalizer-2.23-08.orig/preserve.c
+++ webalizer-2.23-08/preserve.c
@@ -57,6 +57,8 @@
 #include "preserve.h"
 
 struct hist_rec hist[HISTSIZE];              /* history structure array   */
+extern u_long resp_counter;                               /* total 404 counter     */
+extern struct response_url * respnotfound;
 
 /*********************************************/
 /* GET_HISTORY - load in history file        */
Index: webalizer-2.23-08/webalizer.c
===================================================================
--- webalizer-2.23-08.orig/webalizer.c
+++ webalizer-2.23-08/webalizer.c
@@ -111,6 +111,9 @@ int     isipaddr(char *);
 /* GLOBAL VARIABLES                          */
 /*********************************************/
 
+struct response_url * respnotfound;
+struct responsetmp_url * respnotfoundtmp;
+u_long resp_counter;                               /* total 404 counter     */
 char    *version     = "2.23";                /* program version          */
 char    *editlvl     = "08";                  /* edit level               */
 char    *moddate     = "26-Aug-2013";         /* modification date        */
Index: webalizer-2.23-08/webalizer.h
===================================================================
--- webalizer-2.23-08.orig/webalizer.h
+++ webalizer-2.23-08/webalizer.h
@@ -144,11 +144,8 @@ struct response_code {     char    *desc
 /* Response URL structure */
 struct response_url { char respurl[MAXURLH];       /* resp url struct       */
 			u_long    count; };
-struct response_url * respnotfound;
 struct responsetmp_url { char respurl[MAXURLH];    /* temp resp url struct  */
 			u_long    count; };
-struct responsetmp_url * respnotfoundtmp;
-u_long resp_counter;                               /* total 404 counter     */
 
 /* Country code structure */
 struct	country_code {u_int64_t idx;              /* TLD index number     */