/usr/lib/gcc-cross/s390x-linux-gnu/5/libitm.so is in libgcc-5-dev-s390x-cross 5.5.0-12ubuntu1cross1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/gcc-cross/s390x-linux-gnu/5/../../../../s390x-linux-gnu/lib/libitm.so.1