Squashed 'src/leveldb/' changes from 113db4962b..aba469ad6a

aba469ad6a Merge bitcoin-core/leveldb-subtree#54: Fix clang thread-safety-pointer warnings
7daf4ed575 Fix clang thread-safety-pointer warnings

git-subtree-dir: src/leveldb
git-subtree-split: aba469ad6a808da8381edf83a99e5ece18958b31

Author: fanquake

util/cache.cc

@@ -171,8 +171,8 @@ class LRUCache {
  private:
   void LRU_Remove(LRUHandle* e);
   void LRU_Append(LRUHandle* list, LRUHandle* e);
-  void Ref(LRUHandle* e);
-  void Unref(LRUHandle* e);
+  void Ref(LRUHandle* e) EXCLUSIVE_LOCKS_REQUIRED(mutex_);
+  void Unref(LRUHandle* e) EXCLUSIVE_LOCKS_REQUIRED(mutex_);
   bool FinishErase(LRUHandle* e) EXCLUSIVE_LOCKS_REQUIRED(mutex_);
 
   // Initialized before use.