autoconf workaround for Mac OSX

Suppress libtool warnings "linking libtool libraries
using a non-POSIX" that eventually made configure fail.

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

Mac OSX does not support anonymous semaphores (sem_init()
and sem_destroy() are stubs) hence switch to using condition
variables for the component message pump to wait for new
messages.

Signed-off-by: Cedric Hombourger <chombourger@gmail.com>
remove use of fstatat()

Mac OSX does not have fstatat() hence construct the absolute
path of each matching readdir() entry and call lstat().

Signed-off-by: Cedric Hombourger <chombourger@gmail.com>
introduce xc_sem_t type and xc_sem ops

Signed-off-by: Cedric Hombourger <chombourger@gmail.com>
use xc_sem_t instead of POSIX semaphores

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