/usr/lib/x86_64-linux-gnu/libQt5WaylandCompositor.so.5.7 is in libqt5waylandcompositor5 5.7.1~20161021-2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libQt5WaylandCompositor.so.5.7.1