When compiling IoTivity with WITH_CLOUD=true

When compiling IoTivity with WITH_CLOUD=true

Aircon_controlee example fails to compile:
In file included from cloud/samples/client/airconditioner/aircon_controlee.cpp:12:0:
resource/csdk/resource-directory/include/RDClient.h:49:21: error: 'recursive_mutex' is not a member of 'std'
     std::shared_ptr<std::recursive_mutex> _csdkLock;

Including the mutex header fixes the issue.

https://github.sec.samsung.net/RS7-IOTIVITY/IoTivity/pull/679
(cherry-picked from 942b81212d584d4471afb6af80aa54d170da80cf)

Change-Id: Ib03099dfdf8dee60439e4fffab579f45bd5978d2
Signed-off-by: Kush <kush.agrawal@samsung.com>
Signed-off-by: Sudipto <sudipto.bal@samsung.com>