sgabios:Makefile: fix issues of build reproducibility

It is desirable to produce the same bits on subsequent
builds when the actual code of the package doesn't
change. (bsc#1011213)

Signed-off-by: Bruce Rogers <brogers@suse.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>
---
 Makefile |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/Makefile
+++ b/Makefile
@@ -14,10 +14,10 @@
 #
 # $Id$
 
-BUILD_DATE = \"$(shell date -u)\"
-BUILD_SHORT_DATE = \"$(shell date -u +%D)\"
-BUILD_HOST = \"$(shell hostname)\"
-BUILD_USER = \"$(shell whoami)\"
+BUILD_DATE = \"$(shell date --date='@$(PACKAGING_TIMESTAMP)' -u)\"
+BUILD_SHORT_DATE = \"$(shell date --date='@$(PACKAGING_TIMESTAMP)' -u +%D)\"
+BUILD_HOST = \"buildhost\"
+BUILD_USER = \"geeko\"
 
 CFLAGS := -Wall -Os -m32 -nostdlib