`rustc_layout_scalar_valid_range_end` does not affect niches 

`Works` properly has a niche of 1, while `DoesNotWork` has no niches even though it should
```rs

#[rustc_layout_scalar_valid_range_start(1)]
pub struct Works {
  private: u32,
}
#[rustc_layout_scalar_valid_range_end(0xFFFF_FF00)]
pub struct DoesNotWork {
  private: u32,
}
```