Update buildroot to 2021.02.1 (#1312)

Signed-off-by: Stefan Agner <stefan@agner.ch>

buildroot/support/download/helpers

@@ -59,7 +59,7 @@ mk_tar_gz() {
     LC_ALL=C sort <"${tmp}.list" >"${tmp}.sorted"
 
     # Create POSIX tarballs, since that's the format the most reproducible
-    tar cf - --transform="s#^\./#${base_dir}/#" \
+    tar cf - --transform="s#^\./#${base_dir}/#S" \
              --numeric-owner --owner=0 --group=0 --mtime="${date}" \
              --format=posix --pax-option="${pax_options}" \
              -T "${tmp}.sorted" >"${tmp}.tar"