Linux 3.16 compat: smp_mb__after_clear_bit()

The smp_mb__{before,after}_clear_bit functions have been renamed
smp_mb__{before,after}_atomic.  Rather than adding a compatibility
function to handle this the code has been updated to use smp_wmb().

This has the advantage of being a stable functionally equivalent
interface.  On many architectures smp_mb__after_clear_bit() expands
to smp_wmb().  Others might be able to do something slightly more
efficient but this will be safe and correct on all of them.

Signed-off-by: Turbo Fredriksson <[email protected]>
Signed-off-by: Brian Behlendorf <[email protected]>
Closes openzfs#386

module/spl/spl-kmem.c

@@ -2365,7 +2365,7 @@ spl_kmem_cache_reap_now(spl_kmem_cache_t *skc, int count)
 
  spl_slab_reclaim(skc, count, 1);
  clear_bit(KMC_BIT_REAPING, &skc->skc_flags);
- smp_mb__after_clear_bit();
+ smp_wmb();
  wake_up_bit(&skc->skc_flags, KMC_BIT_REAPING);
 out:
  atomic_dec(&skc->skc_ref);