[gtk-vnc] Add stddef.h for size_t on FreeBSD.

[Daniel P. Berrange <dberrange src gnome org>]

commit 16b5ed3e4237668a8f352c0a1408e2460c5c1e89
Author: Koop Mast <kwm rainbow-runner nl>
Date:   Sat Dec 14 23:27:11 2013 +0100

    Add stddef.h for size_t on FreeBSD.

 src/continuation.h |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/src/continuation.h b/src/continuation.h
index 46f7a71..a416837 100644
--- a/src/continuation.h
+++ b/src/continuation.h
@@ -22,6 +22,7 @@
 #define _CONTINUATION_H_
 
 #include <ucontext.h>
+#include <stddef.h>
 
 struct continuation
 {