--- HOWTO ---
If your package uses config.guess and/or config.sub, then it probably
relies on the autotools as its build system. In this case, you should
use the AUTOTARGETS infrastructure, which will take care of updating
the config.guess and/or config.sub files appropriately. See the
Buildroot documentation for details about the AUTOTARGETS
infrastructure.

If for some reason your package does not use the AUTOTARGETS
infrastructure, you can request the config.guess and/or config.sub
files of your package to be updated by using:

      $(call CONFIG_UPDATE,directory-of-your-package-sources)

--- UPDATE ---
GNU config is now managed in git, so to update:

# git clone git://git.savannah.gnu.org/config.git
# cp config/config.* .
# for p in $(ls patches/*.patch); do patch -p0 < $p; done
# rm -rf config

A few local customizations are used to support uClibc so you may
have to make sure they're still needed.  The patches are broken
out in the patches/ dir to keep things simple.