add memory barriers before evaluating RDR_Depleted()

src/varnishevent.c

@@ -145,6 +145,7 @@ RDR_Stats(void)
 int
 RDR_Depleted(void)
 {
+    VWMB();
     return (rdr_tx_free < tx_thresh) || (rdr_rec_free < rec_thresh)
         || (rdr_chunk_free < chunk_thresh);
 }

src/writer.c

@@ -250,6 +250,7 @@ wrt_write(tx_t *tx)
 
     assert(tx->state == TX_FREE);
 
+    VRMB();
     if (RDR_Depleted() || wrt_nfree_tx > tx_thresh
         || wrt_nfree_recs > rec_thresh || wrt_nfree_chunks > chunk_thresh)
         wrt_return_freelist();