cmd/go: add version of GOROOT to go bug details

Fixes #15877.

Change-Id: Ia1e327c0cea3be43e5f8ba637c97c223cee4bb5a
Reviewed-on: https://go-review.googlesource.com/32643
TryBot-Result: Gobot Gobot <gobot@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Author: rsc

src/cmd/go/bug.go

@@ -44,6 +44,7 @@ func runBug(cmd *Command, args []string) {
 	for _, e := range env {
 		fmt.Fprintf(&buf, "%s=\"%s\"\n", e.name, e.value)
 	}
+	printGoDetails(&buf)
 	printOSDetails(&buf)
 	printCDetails(&buf)
 	fmt.Fprintln(&buf, "```")
@@ -72,6 +73,11 @@ A link on play.golang.org is best.
 
 `
 
+func printGoDetails(w io.Writer) {
+	printCmdOut(w, "GOROOT/bin/go version: ", filepath.Join(runtime.GOROOT(), "bin/go"), "version")
+	printCmdOut(w, "GOROOT/bin/go tool compile -v: ", filepath.Join(runtime.GOROOT(), "bin/go"), "tool", "compile", "-V")
+}
+
 func printOSDetails(w io.Writer) {
 	switch runtime.GOOS {
 	case "darwin":