[IA64] export account_system_vtime

The symbol account_system_vtime is used by the kvm module but
not exported.  This breaks building with CONFIG_VIRT_CPU_ACCOUNTING
and CONFIG_KVM=m.
Signed-off-by: Doug Chapman <doug.chapman@hp.com>
Acked-by: Hidetosho Seto <seto.hidetoshi@jp.fujitsu.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>

arch/ia64/kernel/time.c

@@ -117,6 +117,7 @@ void account_system_vtime(struct task_struct *tsk)
 
 	local_irq_restore(flags);
 }
+EXPORT_SYMBOL_GPL(account_system_vtime);
 
 /*
  * Called from the timer interrupt handler to charge accumulated user time