This configuration includes all developer options, so we are sure that
./MAKEALL is build-testing all the code (excluding the very-reduced
pp_printf implementations).

If you want to check which config options are used, please run

  grep '^config' Kconfig | tr '[a-z] ' '[A-Z]_' | while read n; do
    echo =========== $n
    grep -rhl "$n=" configs/*
  done
Signed-off-by: Alessandro Rubini <rubini@gnudd.com>