[llvm] [MachineSink] Only add sink candidate if toBB is a successor of fromBB (PR #98540)

[Alexander Kornienko via llvm-commits]

alexfh wrote:

> > Also, please add tests.
> 
> See [#98477 (comment)](https://github.com/llvm/llvm-project/issues/98477#issuecomment-2223068608).

Also https://github.com/llvm/llvm-project/pull/97618#issuecomment-2223340466 ;)

https://github.com/llvm/llvm-project/pull/98540