(SOSLOCK): Remove
(SOSUNLOCK): Ditto.
(LOCK): Ditto
(UNLOCK): Ditto.
(sos_alloc): If HAVE_CMPXCHG is defined, use cmpxchg_ptr() to atomically allocate
memory in a lock-free manner. Otherwise, fall back on disabling signal
delivery and holding the sos_lock during memory allocation.
(sos_free): Remove.
(mempool_init): Initialize pool lock. Replace LOCK/UNLOCK with appropriate
signal-masking & mutex_lock/unlock calls.
(mempool_free): Replace LOCK/UNLOC with appropriate signal-masking & mutex_lock/unlock
calls.
(Logical change 1.59)