/usr/lib/x86_64-linux-gnu/libnanomsg.so is in libnanomsg-dev 0.8~beta+dfsg-1+b1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libnanomsg.so.4.0.0
/usr/lib/x86_64-linux-gnu/libnanomsg.so.4.0.0