Minimal change to get it to build. There's lots more like this...

--- uudeview-0.5.20/inews/inews.c	2004-01-29 02:14:19.000000000 +0000
+++ uudeview-0.5.20/inews/inews.c	2025-07-04 05:52:21.359784120 +0100
@@ -43,6 +43,8 @@
 
 #define	MAX_SIGNATURE	6
 
+void append_signature(void);
+
 extern	FILE	*ser_wr_fp;
 
 char	host_name[256];
@@ -181,6 +183,7 @@
  * The rn-style DOTDIR environmental variable is used if present.
  */
 
+void
 append_signature()
 {
 	char	line[256], sigfile[256];