/usr/lib/gcc/x86_64-linux-gnu/5/libasan.so is in libgcc-5-dev 5.5.0-12ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/gcc/x86_64-linux-gnu/5/../../../x86_64-linux-gnu/libasan.so.2
/usr/lib/gcc/x86_64-linux-gnu/5/../../../x86_64-linux-gnu/libasan.so.2