/usr/lib/x86_64-linux-gnu/libirstlm.so is in libirstlm-dev 5.80.03-2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libirstlm.so.0.0.0
/usr/lib/x86_64-linux-gnu/libirstlm.so.0.0.0