Description:
------------
Whenever var_export() is called on the result of FFI::new(), PHP segfaults.

I think it's related to calling GC_PROTECT_RECURSION, *but the line numbers in my build may be wrong*

```
 553                                             GC_PROTECT_RECURSION(myht);
(gdb) bt
#0  0x0000000000944811 in php_var_export_ex (struc=0x7fffecc13100, level=1, buf=0x7fffffffbf90) at /path/to/php-src/ext/standard/var.c:553
#1  0x0000000000944fe3 in zif_var_export (execute_data=0x7fffecc130b0, return_value=0x7fffffffbfe0) at /path/to/php-src/ext/standard/var.c:622
#2  0x0000000000bb2b63 in ZEND_DO_ICALL_SPEC_RETVAL_UNUSED_HANDLER () at /path/to/php-src/Zend/zend_vm_execute.h:649
```

Test script:
---------------
```
» php -a
Interactive shell

php > $x = FFI::new('int');
php > echo gettype($x);
object
php > echo get_class($x);
FFI\CData
php > var_dump($x);
object(FFI\CData:int32_t)#1 (1) {
  ["cdata"]=>
  int(0)
}
php > var_export($x);
[1]    2615 segmentation fault  php -a
```

Expected result:
----------------
Either dumps the type or throws an Exception/Error for being impossible to dump

Actual result:
--------------
Segfaults