Comment # 7 on bug 111272 from Michel Dänzer

Due to DRI_PRIME=1, libGL tries to initialize the i965 driver with DRI3, which
fails:

 libGL error: Different GPU, but blitImage not implemented for this driver
 libGL error: failed to load driver: i965

So it falls back to DRI2, which uses the AMD GPU, because the Intel one wasn't
initialized in Xorg. DRI2 doesn't support sync-to-vblank via PRIME.

Reassigning to Mesa for now, but DRI_PRIME=1 really isn't intended to be used
with a single GPU.