Description:
------------
I'm not sure if this can be called a bug, unexpected or undefined behavior - but behavior for the test case below changed in PHP 8.0.

The file below "a.php" implements this pattern: 1. include another file "b.php". 2. declare a class. If that class contains a method "__toString()", the class won't be available yet in b.php. I don't know if this is the direct cause or merely a symptom of compiler behavior.

The example is a bit contrived but it demonstrates the changed behavior clearly. It was encountered and extracted when upgrading a legacy php library (nusoap).

Test script:
---------------
File: a.php

```
    <?php

    include('b.php');

    class a
    {
        public function __toString()
        {
            return '';
        }
    }
```

File: b.php

```
    <?php var_dump(class_exists('a'));
```

Expected result:
----------------
> php a.php
bool(true)

Actual result:
--------------
On PHP 7.4:
bool(true)

On PHP 8.0:
bool(false)