Fix destruction order in zend_shutdown (bug #65463, #66036)

If Apache or a similar SAPI receives a signal during PHP processing
it calls zend_shutdown() without calling shutdown_executor().
	#65463: If a module like Gearman or Memcached is loaded,
in the unfixed version it is unloaded by zend_destroy_modules() before the
CG(CLASS_TABLE) is destructed. When CG(CLASS_TABLE) is destructed,
any pointers to methods (specifically around destruction) in the unloaded
module's .so are now dangling and the process segfaults.
	#66036: Any subclasses of an internal class like ArrayObject need
to be destructed in order: subclass first and then the internal class. In the
unfixed version zend_shutdown() clears the CG(CLASS_TABLE) from the head
of the list onwards, so internal classes are destructed first and user-defined
classes last. Internal classes are alloc/deallocated with malloc/free while
user-defined classes with emalloc/efree. If there's shared data between them
then efree() could be called instead of free() leading to a seg-fault.