Reduce usage of __DATE__

Reduce usage of __DATE__

To increase the reproducibility of builds
we shouldn't use __DATE__. However, for
the development builds there is some demand
for leaving this in.

So as suggested by Gert Doering go for a
compromise where we only use __DATE__ if
we also include the git information. This
will remove this information from release
builds, but not from builds done directly
from the git checkout.

Signed-off-by: Frank Lichtenheld <frank@lichtenheld.com>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20220804150301.62856-2-frank@lichtenheld.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg24807.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>