Set the language to C++ when checking for Boost libraries.

Set the language to C++ when checking for Boost libraries.

The Boost libraries are written in C++ so it is best to set the
language as C++ when running the SCons Configure.CheckLib(boost_...)
tests.

Change-Id: I64f4d9cd1baebed8080fa7cfde375bafe7de19f8
Signed-off-by: Ossama Othman <ossama.othman@intel.com>
Signed-off-by: Erich Keane <erich.keane@intel.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/1022
Reviewed-by: Caiwen Zhang <caiwen.zhang@intel.com>
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>