re PR c++/67130 (ICE: tree check: expected identifier_node, have template_decl in write_unqualified_id, at cp/mangle.c:1218)

	PR c++/67130
	PR c++/67131
	PR c++/66260
	* mangle.c (write_expression) [TEMPLATE_ID_EXPR]: Handle variable
	templates.
	* pt.c (tsubst_copy_and_build): Check for argument substitution
	failure.

From-SVN: r226676