Symfony\Tests\Component\Locale\LocaleTest->testGetDisplayCountriesReturnsFullListForSubLocale()
fails with a fatal error if the PHP extension 'intl' is not installed on the system.
Added a check which skips the affected tests if the extension is not available.
Fixes#3139
Sublocales like de_CH returned only incomplete results for
getDisplayCountries(), getDisplayLanguages() and getDisplayLocales(),
consisting only of results specific for this sublocale, but without the
results of their respective parent locale