THRIFT-856. cpp: Building cpp library fails on OS X with malloc and free not being declared in scope

This patch adds include which seems to fix the problem for some people.

Patch: James Clarke

git-svn-id: https://svn.apache.org/repos/asf/incubator/thrift/trunk@992013 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/lib/cpp/src/Thrift.cpp b/lib/cpp/src/Thrift.cpp
index cc0a01b..114947f 100644
--- a/lib/cpp/src/Thrift.cpp
+++ b/lib/cpp/src/Thrift.cpp
@@ -19,6 +19,7 @@
 
 #include <Thrift.h>
 #include <cstring>
+#include <cstdlib>
 #include <boost/lexical_cast.hpp>
 #include <stdarg.h>
 #include <stdio.h>