A recent addition to the DRM tree for 4.7 added 'extern "C"' guards
for c++ to all the DRM headers, and that now causes warnings
in 'make headers_check':

usr/include/drm/amdgpu_drm.h:38: userspace cannot reference function or variable defined in the kernel
usr/include/drm/drm.h:63: userspace cannot reference function or variable defined in the kernel
usr/include/drm/drm.h:699: userspace cannot reference function or variable defined in the kernel
usr/include/drm/drm_fourcc.h:30: userspace cannot reference function or variable defined in the kernel
usr/include/drm/drm_mode.h:33: userspace cannot reference function or variable defined in the kernel
usr/include/drm/drm_sarea.h:38: userspace cannot reference function or variable defined in the kernel
usr/include/drm/exynos_drm.h:21: userspace cannot reference function or variable defined in the kernel
usr/include/drm/i810_drm.h:7: userspace cannot reference function or variable defined in the kernel

This changes the...