Previously the case
EBB | \_ | | | TBB | / FBB
was treated as a valid triangle also when TBB and FBB was the same basic
block. This could then lead to an invalid CFG when we removed the edge
from EBB to TBB, since that meant we would also remove the edge from EBB
Since TBB == FBB is quite a degenerated case of a triangle, we now
don't treat it as a valid triangle anymore, and thus we will avoid the
trouble with updating the CFG.