Apparently a commit that I can’t find (“e8de9e9“?) disabled acceleration for R5 240 Radeon cards, but causes an error for R7 models.  If you’ve got an R5 and you want accelerated video, try taking it out – assuming it’s not working already.  Any other Radeon model, it may not make a difference.

Update: Pierre Alain-TORET found the correct commit.