/usr/mips64el-linux-gnuabi64/lib/librt.so.1 is in libc6-mips64el-cross 2.24-10cross1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/mips64el-linux-gnuabi64/lib/librt-2.24.so
/usr/mips64el-linux-gnuabi64/lib/librt-2.24.so