Fixed a few problems found on linux x86_64 version


git-svn-id: https://svn.apache.org/repos/asf/incubator/thrift/trunk@664728 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/lib/cpp/src/concurrency/Util.h b/lib/cpp/src/concurrency/Util.h
index d04435d..8467a2c 100644
--- a/lib/cpp/src/concurrency/Util.h
+++ b/lib/cpp/src/concurrency/Util.h
@@ -2,6 +2,7 @@
 #define _concurrency_Util_h_ 1
 
 #include <assert.h>
+#include <stddef.h>
 #include <sys/time.h>
 
 namespace facebook { namespace thrift { namespace concurrency {