https://sourceforge.net/p/byaccj/patches/5/

main.c: In function ‘done’:
main.c:88:43: error: implicit declaration of function -Werror=implicit-function-declaration
   88 |   if (action_file) { fclose(action_file); unlink(action_file_name); }
      |                                           ^~~~~~
--- a/src/main.c
+++ b/src/main.c
@@ -2,6 +2,8 @@
 #include <stdlib.h>
 #include <string.h>
 
+#include <unistd.h>
+
 #ifndef __WIN32__  /*rwj  --  make portable*/
 #include <signal.h>
 #else