build_clone uses copy_node to duplicate the TEMPLATE_INFO for a clone, but
this clears TREE_CHAIN, which was TI_ARGS in a TEMPLATE_INFO.

	* cp-tree.h (struct tree_template_info): Use tree_base instead of
	tree_common.  Add tmpl and args fields.
	(TI_TEMPLATE, TI_ARGS): Adjust.

From-SVN: r273943