From: Andrei Borzenkov <arvidjaar@gmail.com>

Fix build with flex 2.6.4+. It no more casts fprintf() call to void, resulting in

[  108s] grub_script.yy.c: In function 'yy_fatal_error':
[  108s] grub_script.yy.c:18:22: error: statement with no effect [-Werror=unused-value]
[  108s]  

as grub2 defines fprintf as 0. Change it to explicitly define fprintf as (void)0.

flex commit: https://github.com/westes/flex/commit/a58086a269d3d7367530c1a178644a8e5f1a374f
Index: grub-2.02/grub-core/script/yylex.l
===================================================================
--- grub-2.02.orig/grub-core/script/yylex.l
+++ grub-2.02/grub-core/script/yylex.l
@@ -91,7 +91,7 @@ typedef size_t yy_size_t;
 #define stdin  0
 #define stdout 0
 
-#define fprintf(...) 0
+#define fprintf(...) (void)0
 #define exit(...) grub_fatal("fatal error in lexer")
 #endif