/usr/libx32/libcilkrts.so.5 is in libx32cilkrts5 6.3.0-18+deb9u1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/libx32/libcilkrts.so.5.0.0
/usr/libx32/libcilkrts.so.5.0.0