Makefile: Make the tarball release reproducible.

* Makefile (TAR_REPRODUCIBILITY_OPTIONS): New variable.
$(RELEASE_TARBALL_FILENAME): Invoke tar with the above options.
Invoke gzip with '--no-name', to prevent keeping the file name and
time stamp.

Change-Id: I64cac307c69cbfbdb7132b1f567f1c3f18baad8c