/usr/lib/gcc/x86_64-linux-gnu/4.7/libquadmath.so is in gcc-4.7 4.7.2-5.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/gcc/x86_64-linux-gnu/4.7/../../../x86_64-linux-gnu/libquadmath.so.0
/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../x86_64-linux-gnu/libquadmath.so.0