Never change BINFO_INHERITANCE_CHAIN.

Never change BINFO_INHERITANCE_CHAIN.

	* init.c (emit_base_init): Change modification of
	BINFO_INHERITANCE_CHAIN to an assert.
	* search.c (get_base_distance_recursive): Likewise.
	(get_base_distance): Likewise.
	(lookup_member): Likewise.
	(convert_pointer_to_single_level): Likewise.
	(lookup_field): Likewise.  Lose setting TREE_VIA_* on TREE_LISTs.
	(lookup_fnfields): Likewise.
	* tree.c (propagate_binfo_offsets): Don't call unshare_base_binfos.
	(unshare_base_binfos): Don't call propagate_binfo_offsets.
	(layout_basetypes): Call propagate_binfo_offsets instead of
	unshare_base_binfos.
	* decl.c (xref_basetypes): Call unshare_base_binfos.
	* pt.c (instantiate_class_template): Likewise.
	* tree.c (reverse_path): Remove 'copy' parm; always make a
	temporary copy.
	* class.c (build_vbase_path): Just call it.
	* search.c (compute_access): Likewise.  Don't re-reverse.

From-SVN: r22024