"set but not used" warnings in the kernel

This is way too spammy and there is no consistent effort to clean them up,
that I can see anyway.

As such, I think these warns are doing more damage than help and should be
disabled by default.

Alternatively, perhaps people can step up. I'm pretty sure to date I got
rid of more of these than anyone else.

Comments?
-- 
Mateusz Guzik <mjguzik gmail.com>