Summary:
Otherwise a rebuild is not done if a RocksDB plugin header file is
changed.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/9120

Test Plan:
Build RocksDB with a plugin.
Change a header file of the RocksDB plugin and rebuild.
Signed-off-by: NDennis Maisenbacher <dennis.maisenbacher@wdc.com>

Reviewed By: riversand963

Differential Revision: D32223303

Pulled By: ajkr

fbshipit-source-id: 76d31b10fe915906edc181c7b6398a09b7d079ee