fix compile warnings (#10976)

Summary:
Fixes lots of compile warnings related to missing override specifiers, e.g.
```
./3rdParty/rocksdb/trace_replay/block_cache_tracer.h:130:10: warning: ‘virtual rocksdb::Status rocksdb::BlockCacheTraceWriterImpl::WriteBlockAccess(const rocksdb::BlockCacheTraceRecord&, const rocksdb::Slice&, const rocksdb::Slice&, const rocksdb::Slice&)’ can be marked override [-Wsuggest-override]
  130 |   Status WriteBlockAccess(const BlockCacheTraceRecord& record,
      |          ^~~~~~~~~~~~~~~~
./3rdParty/rocksdb/trace_replay/block_cache_tracer.h:136:10: warning: ‘virtual rocksdb::Status rocksdb::BlockCacheTraceWriterImpl::WriteHeader()’ can be marked override [-Wsuggest-override]
  136 |   Status WriteHeader();
      |          ^~~~~~~~~~~
```

Pull Request resolved: https://github.com/facebook/rocksdb/pull/10976

Reviewed By: riversand963

Differential Revision: D41478588

Pulled By: ajkr

fbshipit-source-id: d30b0457241999e38b16aacf6dabe3e691f7c46f

trace_replay/block_cache_tracer.h

@@ -129,11 +129,11 @@ class BlockCacheTraceWriterImpl : public BlockCacheTraceWriter {
   // Pass Slice references to avoid copy.
   Status WriteBlockAccess(const BlockCacheTraceRecord& record,
                           const Slice& block_key, const Slice& cf_name,
-                          const Slice& referenced_key);
+                          const Slice& referenced_key) override;
 
   // Write a trace header at the beginning, typically on initiating a trace,
   // with some metadata like a magic number and RocksDB version.
-  Status WriteHeader();
+  Status WriteHeader() override;
 
  private:
   SystemClock* clock_;