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 <[email protected]>

Author: targos

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

@@ -4,6 +4,5 @@ require('../common');
 constassert=require('assert');
 constconfig=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/');