* expr.c (expand_assignment): Disable the bitfield += optimizations.

	* gcc.c-torture/execute/20040629-1.c (FIELDS1, FIELDS2): Define to
	nothing if not yet defined.  Use it in b, c and d type definitions.
	* gcc.c-torture/execute/20040705-1.c: New test.
	* gcc.c-torture/execute/20040705-2.c: New test.

From-SVN: r84133