folly::ConcurrentHashMapSIMD - fix use after free

Summary: The current order of retire and reclaim_nodes in clear() introduces a subtle bug which allows the hazptr library to destroy the Chunks array from reclaim_nodes, freeing the memory at chunks_, then continue reclaiming nodes which involves further access to chunks_.`

Reviewed By: magedm

Differential Revision: D14968860

fbshipit-source-id: 1bc8e543ae54c3d0e26affb1fd352c58cc5ce897

folly/concurrency/detail/ConcurrentHashMap-detail.h

@@ -1351,8 +1351,8 @@ class alignas(64) SIMDTable {
       chunks_.store(newchunks, std::memory_order_release);
       size_ = 0;
     }
-    chunks->retire(HazptrTableDeleter(ccount));
     chunks->reclaim_nodes(ccount);
+    chunks->retire(HazptrTableDeleter(ccount));
   }
 
   void max_load_factor(float factor) {