Fix build of cc1 for pdp11

[Paul Koning]

Looks good.

	paul

On Sep 14, 2010, at 7:34 PM, Joseph S. Myers wrote:

> The pdp11 back end has its own register_move_cost function that
> conflicts with the target-independent one added a few months ago.
> This patch fixes build of cc1 for this target by renaming the target's
> function to pdp11_register_move_cost.
> 
> Tested with building cc1 for cross to pdp11-none.  OK to commit?