main: rework preprocessor invocation

[cparser] / lextest / do_tests.sh

#!/bin/sh
cd `dirname $0`
for i in tokenstreams/*; do
        if [ "$i" != "tokenstreams/refresults" ]; then
                echo "==> Checking $i"
                ../cparser --lextest $i > /tmp/tokenstream
                diff -u tokenstreams/refresults/`basename $i` /tmp/tokenstream
        fi
done