Fix FFI test on Windows

Author: nikic

ext/ffi/tests/042.phpt

@@ -10,7 +10,7 @@ $a = FFI::new("uint8_t[8]");
 $a[] = 0;
 ?>
 --EXPECTF--
-Fatal error: Uncaught FFI\Exception: Cannot add next element to object of type FFI\CData in %sext/ffi/tests/042.php:3
+Fatal error: Uncaught FFI\Exception: Cannot add next element to object of type FFI\CData in %s:3
 Stack trace:
 #0 {main}
-  thrown in %sext/ffi/tests/042.php on line 3
+  thrown in %s on line 3