u-boot-libre: Add reproducible builds and tests

The tar options come from the tutorial to remove archives metadata at
reproducible-builds.org[1].

[1]https://reproducible-builds.org/docs/archives/

Signed-off-by: Denis 'GNUtoo' Carikli <GNUtoo@cyberdimension.org>

resources/scripts/build/release/u-boot-libre

@@ -48,7 +48,13 @@ rm -rf ${tmpdir}/.git ${tmpdir}/.gitignore
 make -C ${tmpdir} distclean
 
 prefix="$(dirname ${tmpdir} | sed 's#^/*##')/"
-tar cf "${tarball}" "${tmpdir}"  --transform="s#${prefix}##"
+tar cf "${tarball}" "${tmpdir}" \
+    --transform="s#${prefix}##" \
+    --format=gnu \
+    --sort=name \
+    --owner=0 --group=0 --numeric-owner \
+    --mtime="1970-01-01" \
+
 lzip -9 --keep -vv "${tarball}"
 xz   -9 --keep -vv "${tarball}"