t6038-*.sh: Pass the -b (--binary) option to sed on cygwin

t6038-*.sh: Pass the -b (--binary) option to sed on cygwin

The tests using the fuzz_conflict helper function (tests 5-6)
fail on cygwin in the same way they used to on MinGW, prior
to commit ca02ad3. The solution is also the same; passing the
-b (--binary) option to sed, using the SED_OPTIONS variable.
We introduce a new prerequisite SED_STRIPS_CR to use in the
conditional initialisation of SED_OPTIONS, rather than MINGW.
The new prerequisite is set in test-lib.sh for both MinGW and
Cygwin.

Signed-off-by: Ramsay Jones <ramsay@ramsay1.demon.co.uk>
Acked-by: Johannes Sixt <j6t@kdbg.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>