Do not bother with C++11 check on C SDK-only platforms.

Do not bother with C++11 check on C SDK-only platforms.

Some IoTivity platforms, such as Arduino, only require the C SDK.  Do
not bother running the C++11 flag check for those platforms.  This
also addresses a problem where Arduino 1.0.x builds would erroneously
fail due to lack of C++11 support.

Change-Id: I1782a258837850adb65e7219254fdeee259a3cc7
Signed-off-by: Ossama Othman <ossama.othman@intel.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/469
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Jon A. Cruz <jonc@osg.samsung.com>
Reviewed-by: Erich Keane <erich.keane@intel.com>
Reviewed-by: Patrick Lankswert <patrick.lankswert@intel.com>