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