Ticket 49305 - Improve atomic behaviours in 389-ds
    
    Bug Description:  Previously our usage of atomics has ranged from
    "okay" with PR_Atomic, to dangerous with atomic's only being
    partially used. Notablp, PR_Atomic is much slower than gcc's
    __atomic_* operations, especially given the barrier options
    avaliable in gcc for thread sync.
    
    Fix Description:  This replaces most calles to PR_Atomic
    with the correct __atomic types. Importantly, this also
    changes the slapi_counter types to __ATOMIC_RELAXED, which
    removes thread ordering constraints, and allows just "atomics"
    to function.
    
    https://pagure.io/389-ds-base/issue/49305
    
    Author: wibrown
    
    Review by: mreynolds (Thanks!)