Follow-up from "glamor: make sure the correct FBO is cleared"
The following discussion from !330 (merged) should be addressed:
For reference, here are two photos of the graphics corruption when the glClear() is introduced with etnaviv on Vivante GC7000L. Tested with mesa 19.3-rc2 and mesa 20 git master. Commenting out just the glClear() makes Xwayland applications look normal again.