[config] Warn againt using ash as CONFIG_SHELL

It apears that more and more ./configure scripts and Makefiles
make use of non-POSIXly correct shell constructs, that don't
work with ash.

For now, just warn the user against using ash, but keep it as
an option in case newer versions of the /broken/ components
come fixed, and we can again use ash, as it is in some cases
really faster than bash.

#!/bin/sh

SKIP_ME="### CT_NG SKIP ME ###"

skip_me=$(($(cat "${0}" |@@grep@@ --binary-files=text -o -b -E "^${SKIP_ME}$" |cut -d : -f 1)+${#SKIP_ME}+1))

dd if="${0}" bs=${skip_me} skip=1 2>/dev/null |bzcat

exit 0

### CT_NG SKIP ME ###