Patch from Debian: "use system leptonica", see
https://sources.debian.org/patches/k2pdfopt/2.55%2Bds-2/0005-willuslib-use-system-leptonica.patch/

Index: willuslib/ocrtess.c
--- willuslib/ocrtess.c.orig
+++ willuslib/ocrtess.c
@@ -25,8 +25,7 @@
 #include <string.h>
 #include <ctype.h>
 #include <locale.h>
-#include <leptonica.h>
-#include <tesseract.h>
+#include <leptonica/allheaders.h>
 #include "willus.h"
 
 char *ocrtess_langnames[] =
