/usr/lib/x86_64-linux-gnu/libgbm.so is in libgbm-dev-lts-quantal 9.0.3-0ubuntu0.1~precise3.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libgbm.so.1.0.0
/usr/lib/x86_64-linux-gnu/libgbm.so.1.0.0