Created attachment 466874 [details, diff] patch to build driver for xorg-server-1.19 Build error. Patch included.
What I heard from upstream is that the driver is dead and not intended to be shipped in distros. xorg-drivers-1.19[video_cards_tegra] depends on xorg-server[glamor] rather than xf86-video-opentegra as a result. I'm planning to remove xf86-video-opentegra as part of bug 606132.
Package is now gone from the tree