Ignore unreachable basic blocks that remain in the jump table list(s) after basic block pruning has completed. This fixes Bug 28102.
The issues described in bug 28102 were traced to unreachable BB pruning not deleting the associated BB from the jump tables. After several false starts it doesn't appear possible and/or a good idea to remove the BB from the jump table list during pruning, so I ended up modifying the assembler output to ignore unreachable BBs that remain in the jump table lists after pruning.
Please let me know if this is the right approach or if I should be doing this some other way.