/usr/x86_64-linux-gnux32/lib64/libquadmath.so.0 is in lib64quadmath0-x32-cross 8-20180414-1ubuntu2cross1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/x86_64-linux-gnux32/lib64/libquadmath.so.0.0.0