[SimplifyCFG] `markAliveBlocks()`: recognize that normal dest of `invoke`d `noreturn...

[SimplifyCFG] `markAliveBlocks()`: recognize that normal dest of `invoke`d `noreturn` function is `unreachable`

As per LangRef's definition of `noreturn` attribute:
```
noreturn
  This function attribute indicates that the function never returns
  normally, hence through a return instruction.
  This produces undefined behavior at runtime if the function
  ever does dynamically return. nnotated functions may still
  raise an exception, i.a., nounwind is not implied.
```