cmd/vet/all: fix print statement, add platform information

Change-Id: Ibbb89c01f3e812a0602961f959672fcb6523449b
Reviewed-on: https://go-review.googlesource.com/47031
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/vet/all/main.go

@@ -238,9 +238,9 @@ NextLine:
 		default:
 			if !parseFailed {
 				parseFailed = true
-				fmt.Fprintln(os.Stderr, "failed to parse vet output:")
+				fmt.Fprintf(os.Stderr, "failed to parse %s vet output:\n", p)
 			}
-			fmt.Println(os.Stderr, line)
+			fmt.Fprintln(os.Stderr, line)
 		}
 		msg = strings.TrimSpace(msg)