re PR c++/66067 (tree check ICE: accessed elt 1 of tree_vec with 0 elts in write_template_args, at cp/mangle.c:2574)

	PR c++/66067
	* mangle.c (write_nested_name): Limit TYPENAME_TYPE handling to
	TYPE_DECLs.
	* mangle.c (write_template_args): Handle 0 length TREE_VEC.

From-SVN: r225083