apps/progs.pl: use SOURCE_DATE_EPOCH if defined for copyright year
apps/progs.pl: use SOURCE_DATE_EPOCH if defined for copyright year

As with 11d7d903, use SOURCE_DATE_EPOCH for the copyright year if it is
defined, to avoid reproducibility problems.

CLA: trivial

Signed-off-by: Ross Burton <ross.burton@arm.com>
Change-Id: I1bea19070411a69155c43de7082350fb2c499da3

Reviewed-by: Tomas Mraz <2bc6038c3dfca09b2da23c8b6da8ba884dc2dcc2@openssl.org>
Reviewed-by: Paul Dale <ddec78389666b4f7c9b4d110380c848489a3e4aa@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/17601)

openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl