Add amd64 instructions I promised to add for Go 1.6
at the beginning of January.

These may be the last instructions added by hand.
I intend to generate the whole set mechanically for Go 1.7.

Fixes #13822.

Change-Id: I8c6bae2efd25f717f9ec750402e50f408a911d2b
Reviewed-on: https://go-review.googlesource.com/18853Reviewed-by: Rob Pike <r@golang.org>