With the goal of centralizing all tests in the system, this is a
first step to establish a Tests sub-tree. It will contain all of
the unit tests and test harnesses for the various components in the
system.
This change establishes a new set of LibTest based tests for validating
the functionality of our pthread implementation. The first tests added
validate the error handling for the pthread spinlock API:
* pthread_spin_init
* pthread_spin_lock
* pthread_spin_try_lock
* pthread_spin_unlock
* pthread_spin_destroy
