cmd/utils: don't check for stderr redirect on windows

The redirect check did not work on Go 1.6 and below because Stat
returned an error for stdout and stderr. In Go 1.7 Stat works on stdout
but doesn't return anything meaningful, causing cmd/geth test failures
because the message is printed to stderr only. Fix it by printing to
stdout only.

cmd/utils/cmd.go

@@ -23,6 +23,7 @@ import (
 	"os"
 	"os/signal"
 	"regexp"
+	"runtime"
 
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/core"
@@ -52,11 +53,17 @@ func openLogFile(Datadir string, filename string) *os.File {
 // is redirected to a different file.
 func Fatalf(format string, args ...interface{}) {
 	w := io.MultiWriter(os.Stdout, os.Stderr)
+	if runtime.GOOS == "windows" {
+		// The SameFile check below doesn't work on Windows.
+		// stdout is unlikely to get redirected though, so just print there.
+		w = os.Stdout
+	} else {
 		outf, _ := os.Stdout.Stat()
 		errf, _ := os.Stderr.Stat()
 		if outf != nil && errf != nil && os.SameFile(outf, errf) {
 			w = os.Stderr
 		}
+	}
 	fmt.Fprintf(w, "Fatal: "+format+"\n", args...)
 	logger.Flush()
 	os.Exit(1)