ca: fix android KitKat 4.4 support

ca: fix android KitKat 4.4 support

pthread_condattr_setclock() was added in Android 5.0 and IoTivity used
it unconditionally which cause linkage errors on older android versions.
With this patch pthread_condattr_setclock() is only accessed when it is
available with a weak reference. In addition android < 5.0 provides a
private function __pthread_cond_timedwait_relative() which is similar
to pthread_cond_timedwait() use that when available instead.

This should make IoTivity compatible with KitKat devices.

This was tested backported to IoTivity 0.9.2 on an Intel based Android
4.4 Phone and an Arm based Android 5.0 Phone.

Change-Id: Ibae6613a4ae52e230b7850ef1a2bad0b5fd530df
Signed-off-by: Hauke Mehrtens <hauke.mehrtens@lantiq.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/2565
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Patrick Lankswert <patrick.lankswert@intel.com>