/usr/include/x86_64-linux-gnu/ is in libqt5webchannel5-dev 5.9.5-0ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/x86_64-linux-gnu/qt5/
/usr/include/x86_64-linux-gnu/qt5/QtWebChannel/
/usr/include/x86_64-linux-gnu/qt5/QtWebChannel/QQmlWebChannel
/usr/include/x86_64-linux-gnu/qt5/QtWebChannel/QWebChannel
/usr/include/x86_64-linux-gnu/qt5/QtWebChannel/QWebChannelAbstractTransport
/usr/include/x86_64-linux-gnu/qt5/QtWebChannel/QtWebChannel
/usr/include/x86_64-linux-gnu/qt5/QtWebChannel/QtWebChannelDepends
/usr/include/x86_64-linux-gnu/qt5/QtWebChannel/QtWebChannelVersion
/usr/include/x86_64-linux-gnu/qt5/QtWebChannel/qqmlwebchannel.h
/usr/include/x86_64-linux-gnu/qt5/QtWebChannel/qtwebchannelversion.h
/usr/include/x86_64-linux-gnu/qt5/QtWebChannel/qwebchannel.h
/usr/include/x86_64-linux-gnu/qt5/QtWebChannel/qwebchannelabstracttransport.h
/usr/include/x86_64-linux-gnu/qt5/QtWebChannel/qwebchannelglobal.h