/usr/lib/libgtkglextmm-x11-1.2.so is in libgtkglextmm-x11-1.2-dev 1.2.0-4.1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/libgtkglextmm-x11-1.2.so.0.0.0
/usr/lib/libgtkglextmm-x11-1.2.so.0.0.0