cmd/go: introduce the GOVERSION env variable

This is an extra variable available via 'go env', but not read from the
user's environment. It corresponds to the same string that
runtime.Version returns, assuming a program is built by the same version
of Go.

It's similar to the output of 'go version', but without the "go version"
prefix nor the "$GOOS/$GOARCH" suffix.

The main use case here is tools, which often use 'go env' to query basic
information about the installed Go tree. Its version was one missing
piece of information, which required an extra call to 'go version'
before this change.

Fixes #41116.

Change-Id: I5c9d8c2ba856c816c9f4c462ba73c907b3441445
Reviewed-on: https://go-review.googlesource.com/c/go/+/265637
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>
Reviewed-by: Russ Cox <rsc@golang.org>
Trust: Jay Conrod <jayconrod@google.com>
Trust: Daniel Martí <mvdan@mvdan.cc>

0 files changed, 0 insertions, 0 deletions