dthelp: more coverity fixes

cde/programs/dthelp/parser/pass2/eltdef/eltdef.c

@@ -75,7 +75,7 @@ int main(argc, argv)
       fprintf(stderr, "**** Specify interface file ****\n") ;
       exit(TRUE) ;
       }
-    strncpy(iffile, argv[1], IFLEN) ;
+    strncpy(iffile, argv[1], IFLEN - 1) ;
     initialize() ;
     while (TRUE) {
       m_token = scan() ;

cde/programs/dthelp/parser/pass2/htag2/sdl.c

@@ -6395,7 +6395,7 @@ while (incr)
  * the amount of padding needed in between the vstruct and the first
  * virpage to make everything work
 */
-static int CompressVstruct()
+static void CompressVstruct()
 {
 #define COMPRESS_PAD_LENGTH 10
 char      buffer[BUFSIZ], zTemp[4];

cde/programs/dthelp/parser/pass2/util/entout.c

@@ -72,8 +72,7 @@ void entout(fname)
     int nameindex ;
     LOGICAL start ;
 
-    strncpy(efilename, fname, ENTFILENAME) ;
-    strncpy(&efilename[strlen(efilename)], ".h", 2) ;
+    snprintf(efilename, sizeof(efilename), "%s.h", fname);
     m_openchk(&entfile, efilename, "w") ;
 
     fprintf(entfile, "#include \"entdef.h\"\n") ;