We did not allocate a cache slot for FETCH_CLASS. This is already
fixed on newer PHP versions.

For the sake of simplicity I'm using a separate hashtable, rather
than trying to do hash perturabation on the double strings.

This can happen if there is an EXIT in the call arguments, in which
case the DO_CALL opcode may be eliminated as unreachable.

For now, don't treat FE_FETCH op2 as no-val use. See GH-4982.

https://www.php.net/print_r

> When the return parameter is TRUE, this function will return a string.
> Otherwise, the return value is TRUE.

* PHP-7.2:
  Fixed bug #78747