os/exec: skip TestContextCancel on the Windows XP builder

Updates #17245

Change-Id: I3d7ea362809040fbbba4b33efd57bf2d27d4c390
Reviewed-on: https://go-review.googlesource.com/87257Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/os/exec/exec_test.go

@@ -1005,6 +1005,9 @@ func TestContext(t *testing.T) {
 }
 
 func TestContextCancel(t *testing.T) {
+	if testenv.Builder() == "windows-386-xp" {
+		t.Skipf("known to fail on Windows XP. Issue 17245")
+	}
 	ctx, cancel := context.WithCancel(context.Background())
 	defer cancel()
 	c := helperCommandContext(t, ctx, "cat")