This is a copy of the kconfig code in the kernel (currently 3.13-rc5) tweaked
to suit Buildroot.

To update:
cp -r /usr/src/linux/scripts/kconfig support/kconfig.new
cd support/kconfig.new
cp -a ../kconfig/patches ../kconfig/README.buildroot ../kconfig/.gitignore .
quilt push -a
# Fix any conflict
cd ..
rm -rf kconfig
mv kconfig.new kconfig

Then verify the toplevel targets work:
config
defconfig
menuconfig
xconfig
gconfig
oldconfig