You can't compile glibc-2.3.5 on a RedHat8 (2.4.x) kernel. You have to be running a 2.6.x kernel.
is a very tricky thing to update, by far the easiest thing to do would be to update the system altogether ... using the distro of your choice.
The odds are rather excellent
that your system will be borked by following those directions.
If you really know your stuff and have plenty of spare hair, you can work your way out of it, but this is
the "newbie" forum...