/usr/lib/x86_64-linux-gnu/libquadmath.so.0 is in libquadmath0 6.3.0-18+deb9u1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/x86_64-linux-gnu/libquadmath.so.0.0.0
/usr/lib/x86_64-linux-gnu/libquadmath.so.0.0.0