CMakeLists.txt
==============
cmake_minimum_required(VERSION 3.2)
include(FindPkgConfig)
pkg_check_modules(LIBLIGHTDM REQUIRED liblightdm-qt5-3)

include_directories(
    ${LIBLIGHTDM_INCLUDE_DIRS}
)

add_library(SessionsModel MODULE
    SessionsModel.cpp
    )

target_link_libraries(SessionsModel
    ${LIBLIGHTDM_LDFLAGS}
    )

SessionsModel.cpp
=================
#include <QLightDM/SessionsModel>

void nothing()
{
    QLightDM::SessionsModel* m_model;
    QHash<int, QByteArray> m_roleNames;

    m_model = new QLightDM::SessionsModel();
    m_roleNames = m_model->roleNames();
}