CC3D - Allow building of a binary that is compatible with the OpenPilot
CC3D bootloader to allow easy switching between OpenPilot and
Cleanflight.

Submitted by Alessio Morale -
http://forums.openpilot.org/topic/43569-baseflightcleanflight-ported-to-cc3d/?p=372149
Fix compiler warning when building for non NAZE targets that use the
HMC5883 compass driver.