https://bugs.freedesktop.org/show_bug.cgi?id=97585
--- Comment #2 from Nicolai Hähnle nhaehnle@gmail.com --- This seems to be the crucial message:
libGL: dlopen /usr/lib/x86_64-linux-gnu/dri/radeonsi_dri.so failed (/usr/lib/x86_64-linux-gnu/dri/radeonsi_dri.so: undefined symbol: drmFreeDevice)
drmFreeDevice should be provided by libdrm. You can use `ldd /usr/lib/x86_64-linux-gnu/dri/radeonsi_dri.so` or additional LD_DEBUG flags to check where libdrm.so comes from. Probably something went wrong while installing the PPA.