mesa-9999 now uses nouveau_channel->cur, which was not in the struct in libdrm-2.4.17, so this patch bumps the version requirement in the mesa live ebuild.
Created attachment 228797 [details, diff] bump libdrm version for dependency
seems to be fixed now, required version in the mesa ebuild is >=x11-libs/libdrm-2.4.19, so I'm closing this bug.