In the worst case, you can depressurize the cabin and then open a window (at least, on the aircraft with cockpit side windows that can open -- e.g. for emergency egress). This draws the smoke forward and out the open window, likely clearing the air enough that the flying pilot (presumably on the other side of the cockpit!) can see the instruments & the runway.
I've never had a cockpit window open like this in flight, but from all reports it's a bit loud but not unbearable, and not particularly windy inside the cockpit. If the smoke can be controlled through other means, you'll do those first on the checklist, but in case the other steps don't improve matters, this step is available, at least for aircraft with windows that slide open (e.g. the 737) or can be swung inward (e.g. C-130).