re PR c++/11962 (ICE in type_dependent_expression on omitted second operand to ?: in template argument expression)

	PR c++/11962
	* typeck.c (build_x_conditional_expr): Handle missing middle
	operands in templates.
	* mangle.c (write_expression): Issue errors about attempts to
	mangle a non-existant middle operator to the ?: operator.

	PR c++/11962
	* g++.dg/template/cond2.C: New test.

From-SVN: r72785