/usr/m68k-linux-gnu/lib/libthread_db.so is in libc6-dev-m68k-cross 2.27-3ubuntu1cross1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/m68k-linux-gnu/lib/libthread_db.so.1
/usr/m68k-linux-gnu/lib/libthread_db.so.1