x86: move rsc.io/x86 here

This code was reviewed on its way into rsc.io/x86:

    https://codereview.appspot.com/120710043
    https://codereview.appspot.com/94500043
    https://codereview.appspot.com/95350044
    https://codereview.appspot.com/95300044
    https://codereview.appspot.com/97100047
    https://codereview.appspot.com/93110044
    https://codereview.appspot.com/91170044
    https://codereview.appspot.com/99000043
    https://codereview.appspot.com/98990043
    https://codereview.appspot.com/100180044

Change-Id: Ie69db9b29ec400f663550158b163ec92a00725b4
Reviewed-on: https://go-review.googlesource.com/13972
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
21 files changed