counters: use bson_sync_synchronize() for memory barrier.

Author: Christian Hergert

mongoc/mongoc-counters-private.h

@@ -111,7 +111,7 @@ mongoc_counter_##ident##_reset (void) \
    for (i = 0; i < NCPU; i++) { \
       __mongoc_counter_##ident.cpus[i].slots[COUNTER_##ident%SLOTS_PER_CACHELINE] = 0; \
    } \
-   __sync_synchronize (); \
+   bson_sync_synchronize(); \
 }
 #include "mongoc-counters.defs"
 #undef COUNTER

mongoc/mongoc-counters.c

@@ -238,7 +238,7 @@ mongoc_counters_register (mongoc_counters_t *counters,
    infos->name[sizeof infos->name-1] = '\0';
    infos->description[sizeof infos->description-1] = '\0';
 
-   __sync_synchronize ();
+   bson_sync_synchronize();
 
    counters->n_counters++;
 
@@ -291,6 +291,6 @@ mongoc_counters_init (void)
     * we have initialized the rest of the counters. Don't forget our memory
     * barrier to prevent compiler reordering.
     */
-   __sync_synchronize ();
+   bson_sync_synchronize();
    counters->size = size;
 }