LEVELDB_INCLUDE_DIR - Only when building with LevelDB; directory that contains db.h
LEVELDB_LIBRARY - Only when building with LevelDB; path to libleveldb.a/libleveldb.so/libleveldb.dll.a
LEVELDB_DLL - Only when building with LevelDB on Windows; path to libleveldb.dll
LEVELDB_INCLUDE_DIR - Only when building with LevelDB; directory that contains db.h
LEVELDB_LIBRARY - Only when building with LevelDB; path to libleveldb.a/libleveldb.so/libleveldb.dll.a
LEVELDB_DLL - Only when building with LevelDB on Windows; path to libleveldb.dll