Includes assembly implementations of Sqrt and Dim.

Change-Id: I57472e8d31e2ee74bcebf9f8e818f765eb9b8abf
Reviewed-on: https://go-review.googlesource.com/20936Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>