re PR other/42715 (output_operand: invalid expression as operand)

	PR debug/42715
	* var-tracking.c (use_type): Choose MO_VAL_SET for REGs set
	without a cselib val.
	(count_uses): Accept MO_VAL_SET with no val on stores.
	(add_stores): Likewise.

	* gcc.dg/pr42715.c: New.

From-SVN: r156102