archive/tar: also skip header roundtrip test on nacl

Update #11426

Change-Id: I7abc4ed2241a7a3af6d57c934786f36de4f97b77
Reviewed-on: https://go-review.googlesource.com/11592
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/archive/tar/tar_test.go

@@ -136,7 +136,7 @@ type headerRoundTripTest struct {
 }
 
 func TestHeaderRoundTrip(t *testing.T) {
-	if runtime.GOOS == "windows" || runtime.GOOS == "plan9" {
+	if runtime.GOOS == "windows" || runtime.GOOS == "plan9" || runtime.GOOS == "nacl" {
 		t.Skipf("skipping on %s; issue 11426", runtime.GOOS)
 	}
 	golden := []headerRoundTripTest{