And update two imports in cmd/internal/objfile/disasm.go.
This makes GO15VENDOREXPERIMENT=0 ./make.bash work.
For Go 1.7 we will move it back.

Fixes #14236.

Change-Id: I429c9af4baff8496f83d113b1b03b90e309f4f48
Reviewed-on: https://go-review.googlesource.com/19384Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>