test: make test-intl-no-icu-data more robust

In V8 5.6, String#toLocaleUpperCase can work even when no ICU data is
loaded. Use another method to check the --icu-data-dir option pointing
to an empty directory.

PR-URL: #10992
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>

test/parallel/test-intl-no-icu-data.js

@@ -4,6 +4,5 @@ require('../common');
 const assert = require('assert');
 const config = process.binding('config');
 
-// No-op when ICU case mappings are unavailable.
-assert.strictEqual('ç'.toLocaleUpperCase('el'), 'ç');
+assert.deepStrictEqual(Intl.NumberFormat.supportedLocalesOf('en'), []);
 assert.strictEqual(config.icuDataDir, 'test/fixtures/empty/');