With today's Buildroot master, the following defconfig:

BR2_x86_64=y
BR2_TOOLCHAIN_EXTERNAL=y
BR2_ROOTFS_DEVICE_CREATION_DYNAMIC_EUDEV=y
BR2_PACKAGE_KODI=y
BR2_PACKAGE_KODI_ALSA_LIB=y
BR2_PACKAGE_KODI_AVAHI=y
BR2_PACKAGE_KODI_DBUS=y
BR2_PACKAGE_KODI_LIBBLURAY=y
BR2_PACKAGE_KODI_GOOM=y
BR2_PACKAGE_KODI_RSXS=y
BR2_PACKAGE_KODI_LIBCEC=y
BR2_PACKAGE_KODI_LIRC=y
BR2_PACKAGE_KODI_LIBMICROHTTPD=y
BR2_PACKAGE_KODI_LIBNFS=y
BR2_PACKAGE_KODI_RTMPDUMP=y
BR2_PACKAGE_KODI_LIBSHAIRPLAY=y
BR2_PACKAGE_KODI_LIBSMBCLIENT=y
BR2_PACKAGE_KODI_LIBTHEORA=y
BR2_PACKAGE_KODI_LIBUSB=y
BR2_PACKAGE_KODI_LIBVA=y
BR2_PACKAGE_KODI_WAVPACK=y
BR2_PACKAGE_KODI_AUDIODECODER_MODPLUG=y
BR2_PACKAGE_KODI_AUDIODECODER_NOSEFART=y
BR2_PACKAGE_KODI_AUDIODECODER_SIDPLAY=y
BR2_PACKAGE_KODI_AUDIODECODER_SNESAPU=y
BR2_PACKAGE_KODI_AUDIODECODER_STSOUND=y
BR2_PACKAGE_KODI_AUDIODECODER_TIMIDITY=y
BR2_PACKAGE_KODI_AUDIODECODER_VGMSTREAM=y
BR2_PACKAGE_KODI_AUDIOENCODER_FLAC=y
BR2_PACKAGE_KODI_AUDIOENCODER_LAME=y
BR2_PACKAGE_KODI_AUDIOENCODER_VORBIS=y
BR2_PACKAGE_KODI_AUDIOENCODER_WAV=y
BR2_PACKAGE_KODI_ADDON_XVDR=y
BR2_PACKAGE_KODI_PVR_ARGUSTV=y
BR2_PACKAGE_KODI_PVR_DVBLINK=y
BR2_PACKAGE_KODI_PVR_DVBVIEWER=y
BR2_PACKAGE_KODI_PVR_FILMON=y
BR2_PACKAGE_KODI_PVR_HTS=y
BR2_PACKAGE_KODI_PVR_IPTVSIMPLE=y
BR2_PACKAGE_KODI_PVR_MEDIAPORTAL_TVSERVER=y
BR2_PACKAGE_KODI_PVR_MYTHTV=y
BR2_PACKAGE_KODI_PVR_NEXTPVR=y
BR2_PACKAGE_KODI_PVR_NJOY=y
BR2_PACKAGE_KODI_PVR_PCTV=y
BR2_PACKAGE_KODI_PVR_STALKER=y
BR2_PACKAGE_KODI_PVR_VBOX=y
BR2_PACKAGE_KODI_PVR_VDR_VNSI=y
BR2_PACKAGE_KODI_PVR_VUPLUS=y
BR2_PACKAGE_KODI_PVR_WMC=y
BR2_PACKAGE_KODI_SCREENSAVER_ASTEROIDS=y
BR2_PACKAGE_KODI_SCREENSAVER_BIOGENESIS=y
BR2_PACKAGE_KODI_SCREENSAVER_CRYSTALMORPH=y
BR2_PACKAGE_KODI_SCREENSAVER_GREYNETIC=y
BR2_PACKAGE_KODI_SCREENSAVER_PINGPONG=y
BR2_PACKAGE_KODI_SCREENSAVER_PYRO=y
BR2_PACKAGE_KODI_SCREENSAVER_STARS=y
BR2_PACKAGE_KODI_VISUALISATION_SHADERTOY=y
BR2_PACKAGE_KODI_VISUALISATION_SPECTRUM=y
BR2_PACKAGE_KODI_VISUALISATION_WAVEFORHUE=y
BR2_PACKAGE_KODI_VISUALISATION_WAVEFORM=y
BR2_PACKAGE_XORG7=y
BR2_PACKAGE_XSERVER_XORG_SERVER=y
BR2_PACKAGE_XSERVER_XORG_SERVER_MODULAR=y
BR2_PACKAGE_NVIDIA_DRIVER=y

fails to build with the following error:

In file included from dri2.c:43:0:
./../../dri2/dri2.h:36:39: fatal error: X11/extensions/dri2tokens.h: No such file or directory
compilation terminated.
make[7]: *** [dri2.lo] Error 1

I believe it is not needed to build Kodi to reproduce the build failure.