Fixed a build issue noticed on the mailing list with lib CA

Fixed a build issue noticed on the mailing list with lib CA

As reported by Gabriel Schulhof on the mailing list, he had
an issue compiling liboctbstack directly.  This patch was
submitted by him via the mailing list.

Change-Id: I2083a8875baddabfa6df6287074639f437cfda60
Signed-off-by: Erich Keane <erich.keane@intel.com>
Signed-off-by: Sachin Agrawal <sachin.agrawal@intel.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/875
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Joseph Morrow <joseph.l.morrow@intel.com>