* tree.c (prototype_p, virtual_method_call_p, obj_type_ref_class,
	is_typedef_decl, typedef_variant_p): Constify.
	* tree.h (prototype_p, virtual_method_call_p, obj_type_ref_class,
	is_typedef_decl, typedef_variant_p): Constify.

From-SVN: r223628