/usr/arm-linux-gnueabihf/lib/librt.so is in libc6-dev-armhf-cross 2.24-10cross1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/arm-linux-gnueabihf/lib/librt.so.1
/usr/arm-linux-gnueabihf/lib/librt.so.1