Fix issue where logger files aren't built for Arduino on CA Branch.

Fix issue where logger files aren't built for Arduino on CA Branch.

The logger file has to be built with a C++ compiler so that we can
use Arduino's Serial functions as they are prepared in C++ world. With
a ".c" extension, the CA layer makefiles enforce it to be build with
a C compiler. We are forcing only the logger.c file to built for c++.

Change-Id: If2c17d15ebdb3b9942cb6c8391b4c2f7865b1fcd
Signed-off-by: Joseph Morrow <joseph.l.morrow@intel.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/187
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Sashi Penta <sashi.kumar.penta@intel.com>
Reviewed-by: Sudarshan Prasad <sudarshan.prasad@intel.com>