optimization/6631: Miscompiled structure access

[Janis Johnson]

This is a regression from GCC 3.0 that was exposed by the following cp
patch:

2002-04-30  Mark Mitchell  <mark@codesourcery.com>

	ABI change, returning simple classes from functions.
	* class.c (finish_struct_bits): Only mark TREE_ADDRESSABLE if
	TYPE_HAS_TRIVIAL_INIT_REF is false or
	TYPE_HAS_NONTRIVIAL_DESTRUCTOR is true.

The test passes with optimization on if it is altered by adding a
destructor or a copy constructor to class QSize, or by removing "const"
from "inline const QSize operator+".

I'm not planning to investigate this further, but hope this additional
information will be useful.

Janis