x/tools: clone some files in preparation for alias changes

This CL only copies files and updates build tags.
Substantive changes will come in follow-ups.
This is a workaround for git's lack of rename/copy tracking.

Tested with go1.6, go1.7, and tip (go1.8).

Change-Id: Id88a05273fb963586b228d5e5dfacab32133a960
Reviewed-on: https://go-review.googlesource.com/32630
Reviewed-by: Robert Griesemer <gri@golang.org>
38 files changed