If you select the i810 DRM driver for inclusion as a module or in the kernel with the gentoo-sources ebuild I used today, the compilation aborts with an error of "i810_dma.c:236: too few arguments to function 'do_munmap_Rsmp_07be63c9'". The only solution is to not attempt to include support for the i810 DRM system.
*** This bug has been marked as a duplicate of 7712 ***