The idea to use atomic aligned to cache line for counting finished jobs
is reused, but instead of polling a semaphore was added

 - removed some whitespace noise.
 - cleaned up CMakeLists.txt
 - reintegrated task_manager.c into thread-pool.c
 - cleaned up some unnecessary code

Co-authored-by: Cedric Roux <cedric.roux@eurecom.fr>
Co-authored-by: Mikel Irazabal <mikel.irazabal@openairinterface.com>

Extract thread-pool into a separate CMake library.
Extract utils into a separate CMake library.