Whilst we can't build perl on such a crippled system, there's no excuse for
logical errors in config.sh resulting in an invalid config.h
This is extracted from
[perl #112494] invalid config.h if stdarg.h and varargs.h both missing
https://rt.perl.org/rt3//Ticket/Display.html?id=112494
: now check which varargs header should be included
echo " "
i_varhdr=''
+val=''
case "$valstd" in
"$define")
if `./varargs I_STDARG`; then
$rm_try
;;
*) echo "You don't have <stdarg.h>, not checking for va_copy()." >&4
+ need_va_copy="$undef"
;;
esac