Description:
------------
FFI can be used to define a native PHP callback via Closure instance for traditional C function pointers (hooks) as described in https://www.php.net/manual/en/ffi.examples-callback.php

This works well for simple return types, like void, double, int, etc. But if a C callback has a complex C return-type/struct, then FFI can't assign a callback to it, failing with a message:

  Uncaught FFI\Exception: FFI internal error. Unsupported return type

It would be nice to have an additional CData type check for a PHP callback and perform some run-time checks to allow PHP hook even for that complex callback types.

Test script:
---------------
Here is a pseudo-code for the PHP zend_compile_string callback defined as following:

ZEND_API zend_op_array *(*zend_compile_string)(zval *source_string, char *filename);

        $php->zend_compile_string = function (CData $sourceString, CData $filename): CData {
            echo 'In the hook';
            $code = Core::new('zend_op_array[10]');
            // ... some opcode initialization logic

            return FFI::addr($code);
        };

Expected result:
----------------
No errors about unsupported return type

Actual result:
--------------
Fatal error: Uncaught FFI\Exception: FFI internal error. Unsupported return type