/usr/lib/gcc-cross/arm-linux-gnueabihf/7/libcilkrts.so is in libgcc-7-dev-armhf-cross 7.3.0-16ubuntu3cross1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/gcc-cross/arm-linux-gnueabihf/7/../../../../arm-linux-gnueabihf/lib/libcilkrts.so.5