This is a follow-up to CL 7360.

It was generated with eg and gofmt -r.

The only manual changes are the unembedding in syntax.go
and backporting changes from y.go to go.y.

Passes toolstash -cmp.

Change-Id: I3d6d06ecb659809a4bc8592395d5b9a18967218e
Reviewed-on: https://go-review.googlesource.com/8053Reviewed-by: Russ Cox <rsc@golang.org>
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>