fix c23, see https://bugs.gentoo.org/943851
https://src.fedoraproject.org/rpms/chkrootkit/raw/rawhide/f/chkrootkit-0.57-sighandler-type.patch + remove old style definition
--- a/chklastlog.c
+++ b/chklastlog.c
@@ -77,7 +77,7 @@
 long total_wtmp_bytes_read=0;
 size_t wtmp_file_size;
 uid_t *uid;
-void read_status();
+void read_status(int signum);
 
 struct s_localpwd {
      int numentries;
@@ -213,7 +213,7 @@
 }
 #endif
 
-void read_status() {
+void read_status(int signum) {
    double remaining_time;
    static long last_total_bytes_read=0;
    int diff;
--- a/chkwtmp.c
+++ b/chkwtmp.c
@@ -43,9 +43,7 @@ int main () { return 0; }
 #endif
 #endif
 
-void printit(counter, start, end)
-int counter;
-long start,end;
+void printit(int counter, long start, long end)
 {
 	char		buffer[30];