Fix libcorkscrew once and forall

corkscrew: Fix build with gcc 4.8

gcc 4.8 has a new warning for unused parameters - we need to override
-Werror on that.

Signed-off-by: Bernhard Rosenkränzer <Bernhard.Rosenkranzer@linaro.org>
Signed-off-by: Paul Beeler <sparksco@gmail.com>