/usr/include/osgEarthDrivers/engine_mp/ is in libosgearth-dev 2.4.0+dfsg-6.
This file is owned by root:root, with mode 0o755.
..
/usr/include/osgEarthDrivers/engine_mp/Common
/usr/include/osgEarthDrivers/engine_mp/CustomPagedLOD
/usr/include/osgEarthDrivers/engine_mp/DynamicLODScaleCallback
/usr/include/osgEarthDrivers/engine_mp/FileLocationCallback
/usr/include/osgEarthDrivers/engine_mp/KeyNodeFactory
/usr/include/osgEarthDrivers/engine_mp/LODFactorCallback
/usr/include/osgEarthDrivers/engine_mp/MPGeometry
/usr/include/osgEarthDrivers/engine_mp/MPTerrainEngineNode
/usr/include/osgEarthDrivers/engine_mp/MPTerrainEngineOptions
/usr/include/osgEarthDrivers/engine_mp/QuickReleaseGLObjects
/usr/include/osgEarthDrivers/engine_mp/SerialKeyNodeFactory
/usr/include/osgEarthDrivers/engine_mp/TerrainNode
/usr/include/osgEarthDrivers/engine_mp/TileModel
/usr/include/osgEarthDrivers/engine_mp/TileModelCompiler
/usr/include/osgEarthDrivers/engine_mp/TileModelFactory
/usr/include/osgEarthDrivers/engine_mp/TileNode
/usr/include/osgEarthDrivers/engine_mp/TileNodeRegistry