/usr/mipsisa64r6el-linux-gnuabi64/lib32/librt.so is in libc6-dev-mipsn32-mips64r6el-cross 2.27-3ubuntu1cross1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/mipsisa64r6el-linux-gnuabi64/lib32/librt.so.1