Abort when HHVM 4.0 is detected to output a clear user message, refs #7990

bin/composer

@@ -18,6 +18,11 @@ $xdebug = new XdebugHandler('Composer', '--ansi');
 $xdebug->check();
 unset($xdebug);
 
+if (defined('HHVM_VERSION') && version_compare(HHVM_VERSION, '4.0', '>=')) {
+    echo 'HHVM 4.0 has dropped support for Composer, please use PHP instead. Aborting.'.PHP_EOL;
+    exit(1);
+}
+
 if (function_exists('ini_set')) {
     @ini_set('display_errors', 1);