os: skip atime-going-backwards test on NetBSD for now

That failing test is preventing other tests from running.
Let's see what else is broken.

Updates #19293

Change-Id: I4c5784be94103ef882f29dec9db08d76a48aff28
Reviewed-on: https://go-review.googlesource.com/37492
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matt Layher <mdlayher@gmail.com>

src/os/os_test.go

@@ -1057,14 +1057,22 @@ func testChtimes(t *testing.T, name string) {
 	}
 	postStat := st
 
-	/* Plan 9, NaCl:
-		Mtime is the time of the last change of content.  Similarly, atime is set whenever the
-	    contents are accessed; also, it is set whenever mtime is set.
-	*/
 	pat := Atime(postStat)
 	pmt := postStat.ModTime()
-	if !pat.Before(at) && runtime.GOOS != "plan9" && runtime.GOOS != "nacl" {
-		t.Errorf("AccessTime didn't go backwards; was=%d, after=%d", at, pat)
+	if !pat.Before(at) {
+		switch runtime.GOOS {
+		case "plan9", "nacl":
+			// Ignore.
+			// Plan 9, NaCl:
+			// Mtime is the time of the last change of
+			// content.  Similarly, atime is set whenever
+			// the contents are accessed; also, it is set
+			// whenever mtime is set.
+		case "netbsd":
+			t.Logf("AccessTime didn't go backwards; was=%d, after=%d (Ignoring. See NetBSD issue golang.org/issue/19293)", at, pat)
+		default:
+			t.Errorf("AccessTime didn't go backwards; was=%d, after=%d", at, pat)
+		}
 	}
 
 	if !pmt.Before(mt) {