reproducible: Improve SOURCE_DATE_EPOCH_FALLBACK handling

reproducible: Improve SOURCE_DATE_EPOCH_FALLBACK handling

Ensure the fallback value if used is written to the SDE file
and hence stored in sstate, reducing any confusion within the
code over '0' values.

Bump the HASHEQUIV_VERSION since we've had a ton of trouble
with ensuring this rolls out correctly on the autobuilder so
others may too, take a clean slate for it.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit 53ffffa32b76330835287dfc05d4e4796841af08)
Signed-off-by: Steve Sakoman <steve@sakoman.com>