/usr/lib/gcc/x86_64-linux-gnu/6/x32/libgomp.so is in libx32gcc-6-dev 6.4.0-17ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/gcc/x86_64-linux-gnu/6/x32/../../../../../libx32/libgomp.so.1