cmd/vet: skip another test on Android

Forgot this one in my previous commit.

Change-Id: Ief089e99bdad24b3bcfb075497dc259d06cc727c
Reviewed-on: https://go-review.googlesource.com/10913
Reviewed-by: David Crawshaw <crawshaw@golang.org>

src/cmd/vet/vet_test.go

@@ -91,6 +91,8 @@ func TestTags(t *testing.T) {
 		if strings.HasPrefix(runtime.GOARCH, "arm") {
 			t.Skip("skipping test; no command execution on darwin/%s", runtime.GOARCH)
 		}
+	case "android":
+		t.Skip("skipping test; no go toolchain available")
 	}
 
 	// go build