So that there is a uniformed way to retrieve Go version from a Go
binary, starting from Go 1.4 (see https://golang.org/cl/117040043)

Updates #13507.

Change-Id: Iaa2b14fca2d8c4d883d3824e2efc82b3e6fe2624
Reviewed-on: https://go-review.googlesource.com/17459Reviewed-by: Keith Randall <khr@golang.org>