Set this to true in order to enable the ignoreFromBuild property.
In the case when a NavMeshBuildMarkup is used to change only the area type of an object, overrideIgnore should be set to false so that the ignoreFromBuild property will not have any effect.
If none of the objects in a hierarchy are marked with ignoreFromBuild set to true then no objects in that hierarchy will be ignored while building the NavMesh.