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/1022Reviewed-by: Caiwen Zhang <caiwen.zhang@intel.com>
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>

service/third_party_libs.scons

@@ -49,15 +49,15 @@ if target_os in ['linux', 'tizen']:
 
 		conf = Configure(lib_env)
 
-		if not conf.CheckLib('boost_thread'):
+		if not conf.CheckLib('boost_thread', language='C++'):
 			print 'Did not find boost_thread, exiting!'
 			Exit(1)
 
-		if not conf.CheckLib('boost_system'):
+		if not conf.CheckLib('boost_system', language='C++'):
 			print 'Did not find boost_system, exiting!'
 			Exit(1)
 
-		conf.Finish()
+		lib_env = conf.Finish()
 
 ######################################################################
 # The 'include' path of external libraries