os: do not close syscall.Stdin in TestReadStdin

By calling NewConsoleFile on syscall.Stdin, we wind up closing it when
the function returns, which causes errors when all the tests are run in
a loop. To fix this, we instead create a duplicate handle of stdin.

Fixes #43720.

Change-Id: Ie6426e6306c7e1e39601794f4ff48bbf2fe67502
Reviewed-on: https://go-review.googlesource.com/c/go/+/284140
Run-TryBot: Jason A. Donenfeld <Jason@zx2c4.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Trust: Jason A. Donenfeld <Jason@zx2c4.com>

src/os/os_windows_test.go

@@ -692,7 +692,16 @@ func TestReadStdin(t *testing.T) {
 		poll.ReadConsole = old
 	}()
 
-	testConsole := os.NewConsoleFile(syscall.Stdin, "test")
+	p, err := syscall.GetCurrentProcess()
+	if err != nil {
+		t.Fatalf("Unable to get handle to current process: %v", err)
+	}
+	var stdinDuplicate syscall.Handle
+	err = syscall.DuplicateHandle(p, syscall.Handle(syscall.Stdin), p, &stdinDuplicate, 0, false, syscall.DUPLICATE_SAME_ACCESS)
+	if err != nil {
+		t.Fatalf("Unable to duplicate stdin: %v", err)
+	}
+	testConsole := os.NewConsoleFile(stdinDuplicate, "test")
 
 	var tests = []string{
 		"abc",