Compaction: Restore SetupForCompaction functionality

In facebook/rocksdb#11658, files are no longer controlled by the access_hint_on_compaction_start flag by removing the content of SetupForCompaction.
However, this leads to degradation in compaction read speed when combined with compaction_readahead_size since once a file is opened, in linux, it is hinted with POSIX_FADV_RANDOM.

See #787 for full details.

Add back the default hint to avoid degradation in this scenario.

table/block_based/block_based_table_reader.cc

@@ -1193,7 +1193,9 @@ Status BlockBasedTable::PrefetchIndexAndFilterBlocks(
  return s;
 }
 
-void BlockBasedTable::SetupForCompaction() {}
+void BlockBasedTable::SetupForCompaction() {
+ rep_->file->file()->Hint(FSRandomAccessFile::kNormal);
+}
 
 TablePinningPolicy* BlockBasedTable::GetPinningPolicy() const {
  return rep_->table_options.pinning_policy.get();