/usr/lib/x86_64-linux-gnu/libgsm.so is in libgsm1-dev 1.0.13-4.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libgsm.so.1.0.12
/usr/lib/x86_64-linux-gnu/libgsm.so.1.0.12