PR c++/69560 - wrong alignof(double) on x86.

	CWG 1879 - Inadequate definition of alignment requirement.
	* cp-tree.h (ALIGNOF_EXPR_STD_P): New.
	* typeck.c (cxx_sizeof_or_alignof_type): Add std_alignof parm.
	(cxx_sizeof_expr, cxx_sizeof_nowarn, cxx_alignas_expr)
	(cxx_alignof_expr): Pass it.
	* parser.c (cp_parser_unary_expression): Pass it.
	* pt.c (tsubst_copy): Copy it.
	(tsubst_copy_and_build): Pass it.
	* decl.c (fold_sizeof_expr): Pass it.

From-SVN: r259578