/usr/lib/gcc/x86_64-linux-gnu/4.9/x32/libubsan.so is in libx32gcc-4.9-dev 4.9.2-10+deb8u1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/gcc/x86_64-linux-gnu/4.9/x32/../../../../../libx32/libubsan.so.0