Partial upgrades to core system libraries like libc6 can sometimes lead to ldconfig not found on PATH error. To fix this, first try to find if ldconfig is present somewhere in the system.

find / -name ldconfig

The above command returns the path of ldconfig if found. I got the path as /var/cache/ldconfig.
Now copy the ldconfig to /usr/bin or similar directory which are added to the PATH variable.

sudo cp -r /var/cache/ldconfig /usr/bin/

Now we remove (downgrade) the library that caused this problem. In my case it was libc6_2.11.3-4 which caused the problem. So removing the current one will downgrade to the previous installed version, which is libc6_2.5.1-1eglibc27+0m5.