/usr/include/x86_64-linux-gnu/ is in libqt5websockets5-dev 5.5.1-4build1.
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/usr/include/x86_64-linux-gnu/qt5/
/usr/include/x86_64-linux-gnu/qt5/QtWebSockets/
/usr/include/x86_64-linux-gnu/qt5/QtWebSockets/QMaskGenerator
/usr/include/x86_64-linux-gnu/qt5/QtWebSockets/QWebSocket
/usr/include/x86_64-linux-gnu/qt5/QtWebSockets/QWebSocketCorsAuthenticator
/usr/include/x86_64-linux-gnu/qt5/QtWebSockets/QWebSocketServer
/usr/include/x86_64-linux-gnu/qt5/QtWebSockets/QtWebSockets
/usr/include/x86_64-linux-gnu/qt5/QtWebSockets/QtWebSocketsDepends
/usr/include/x86_64-linux-gnu/qt5/QtWebSockets/QtWebSocketsVersion
/usr/include/x86_64-linux-gnu/qt5/QtWebSockets/qmaskgenerator.h
/usr/include/x86_64-linux-gnu/qt5/QtWebSockets/qtwebsocketsversion.h
/usr/include/x86_64-linux-gnu/qt5/QtWebSockets/qwebsocket.h
/usr/include/x86_64-linux-gnu/qt5/QtWebSockets/qwebsocketcorsauthenticator.h
/usr/include/x86_64-linux-gnu/qt5/QtWebSockets/qwebsocketprotocol.h
/usr/include/x86_64-linux-gnu/qt5/QtWebSockets/qwebsockets_global.h
/usr/include/x86_64-linux-gnu/qt5/QtWebSockets/qwebsocketserver.h