common: adds _GPUCODE guard
common: adds _GPUCODE guard

prevents NS(Buffer) based methods and methods calling offsetof from being visible to GPUCODE like cuda kernels (which can currenlty not make use of it)
SixTrack/SixTrackLib,SixTrack/SixTrackLib,SixTrack/SixTrackLib,SixTrack/SixTrackLib