/usr/lib/x86_64-linux-gnu/libmongoc-1.0.so is in libmongoc-dev 1.9.2+dfsg-1build1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libmongoc-1.0.so.0.0.0
/usr/lib/x86_64-linux-gnu/libmongoc-1.0.so.0.0.0