Use the recently added CPU feature detection API rather than custom assembly. This will need to be updated to use 'internal/cpu' when the package is revendored into std. Change-Id: Ia99c51c7409fe4fabcd88fdf5ff19772c1ca2257 Reviewed-on: https://go-review.googlesource.com/c/164382 Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org> Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org>