/// isLayoutSuccessor - Return true if the specified MBB will be emitted
/// immediately after this block, such that if this block exits by
/// falling through, control will transfer to the specified MBB. Note
/// that MBB need not be a successor at all, for example if this block
/// ends with an unconditional branch to some other block.
/// isLayoutSuccessor - Return true if the specified MBB will be emitted
/// immediately after this block, such that if this block exits by
/// falling through, control will transfer to the specified MBB. Note
/// that MBB need not be a successor at all, for example if this block
/// ends with an unconditional branch to some other block.