Hi Ahish,
You do not need to use the toolchain.gz. I am not even sure what that is, or what it is for.
The LTIB bsp you are using has a much newer toolchain/glibc than the zipped file you are asking about.
It looks like the issue you are running into is with the glibc version on your host PC. The mx21_download utility cannot find a glibc that has the version support it is looking for.
What Linux distribution and version are you running the MX21ADS bsp on?
Coray