add traces for POSIX semaphores

Signed-off-by: Cedric Hombourger <chombourger@gmail.com>
Revert "use condition variables instead of semaphores"

This reverts commit 10e572ae240fbc6c30ed9257b6f5b9f46497ef05.
use xc_sem instead of POSIX semaphores

Signed-off-by: Cedric Hombourger <chombourger@gmail.com>