/usr/lib/x86_64-linux-gnu/libQt5X11Extras.so is in libqt5x11extras5-dev 5.2.1-1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libQt5X11Extras.so.5.2.1
/usr/lib/x86_64-linux-gnu/libQt5X11Extras.so.5.2.1