The words in auxval are encoded in native byte order.

I haven't added a test. This fix will be tested when s390x support
is added to the package.

Change-Id: I276f833660e6906c319995798faf9054ffc69461
Reviewed-on: https://go-review.googlesource.com/c/162902
Run-TryBot: Michael Munday <mike.munday@ibm.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>