https://github.com/01org/opa-ff/pull/10

commit 2ae76192815212d7a3f821d6a3dddc3d0bb9eae4
Author: Bernhard M. Wiedemann <bwiedemann@suse.de>
Date:   Wed Nov 15 20:14:04 2017 +0100

    Allow to override build date
    
    in order to make builds reproducible.
    See https://reproducible-builds.org/ for why this is good
    and https://reproducible-builds.org/specs/source-date-epoch/
    for the definition of this variable.
    This date call only works with GNU date.
    
    Also use UTC to be independent of timezones.
    And use ISO date format as the only proper way to unambiguously
    represent a date.

diff --git a/MakeTools/prep.sh b/MakeTools/prep.sh
index c0a4bd1..52b19a6 100755
--- a/MakeTools/prep.sh
+++ b/MakeTools/prep.sh
@@ -81,6 +81,7 @@ then
 	exit 1
 fi
 
+[[ $SOURCE_DATE_EPOCH ]] && DATE=`date -u -d "@$SOURCE_DATE_EPOCH" -Iseconds`
 DATE=${DATE:-"`date +'%m/%d/%y %H:%M'`"}
 
 if [ "$#" = 1 ]