see http://lists.nongnu.org/archive/html/qemu-devel/2006-02/msg00174.html

--- qemu.org/target-i386/helper2.c      2005-12-04 19:46:06.000000000 +0100
+++ qemu/target-i386/helper2.c  2006-02-18 22:50:37.362222345 +0100
@@ -24,6 +24,7 @@
 #include <inttypes.h>
 #include <signal.h>
 #include <assert.h>
+#include <errno.h>
 
 #include "cpu.h"
 #include "exec-all.h"