HPCC-10379 New semaphore implementation based on sem_xxx

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
HPCC-10379 Add some very simple unit tests for the semaphores

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
Merge pull request #5115 from ghalliday/issue10379

HPCC-10379 New semaphore implementation based on sem_xxx

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>