/usr/lib/x86_64-linux-gnu/libGL.so.1 is in libgl1-mesa-swx11 10.3.2-1+deb8u1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libGL.so.1.6.0
/usr/lib/x86_64-linux-gnu/libGL.so.1.6.0