xbmc requires glxinfo
When I tried to run xbmc from the opkg installation I got an error that glxinfo was not found. glxinfo is not included in the userland tools. I'm guessing that glxinfo, which I think is in the Mesa3D packages needs to be compiled against the userland tools, which means it won't build directly out of buildroot. I've posted a question about this to the Raspberry Pi forums.