bug#27773: [PATCH] Allow to override build date

[Bernhard M. Wiedemann]

and use gmtime to not be influenced by timezone settings
in order to make builds reproducible.

While working on the reproducible builds effort, I found that
when building the automake package for openSUSE Linux,
there were slight differences between each build

See https://reproducible-builds.org/ for why this is matters
and https://reproducible-builds.org/specs/source-date-epoch/
for the definition of this variable.
---
 doc/help2man | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/doc/help2man b/doc/help2man
index e651b8d2d..4a9f75064 100755
--- a/doc/help2man
+++ b/doc/help2man
@@ -217,7 +217,7 @@ $version_text ||= get_option_value $ARGV[0], 
$version_option;
 # the English version expands to the month as a word and the full year.  It
 # is used on the footer of the generated manual pages.  If in doubt, you may
 # just use %x as the value (which should be the full locale-specific date).
-my $date = enc strftime _("%B %Y"), localtime;
+my $date = enc strftime _("%B %Y"), gmtime($ENV{SOURCE_DATE_EPOCH} || time());
 (my $program = $ARGV[0]) =~ s!.*/!!;
 my $package = $program;
 my $version;
-- 
2.12.3