Hi! I'm actually from upstream, and I noticed you guys don't have the latest libwacom in portage when trying to test some patches. The latest version, 0.11, compiles perfectly with the current ebuild in portage. All that needs to be done for it to work is bumping up the version of the ebuild.
+*libwacom-0.11 (17 Feb 2015) + + 17 Feb 2015; Alexandre Rostovtsev <tetromino@gentoo.org> + +libwacom-0.11.ebuild: + Version bump, adds support for cintiq companion (bug #540204, thanks to + Chandler Paul).