[llvm] [IR] Add disjoint flag for Or instructions. (PR #72583)

[Philip Reames via llvm-commits]

preames wrote:

> > I can reduce a test case if needed, but the assertion failure seems fairly self explanatory.
> 
> It might be a separate issue to #74112, so if it would be possible to reduce a test case to check if it is indeed an `or disjoint` that's causing this, that would be helpful. In any case, we should support preserving the new `disjoint` flag, so I put up #74364

Since both of the changes mentioned landed, I pulled them both in and can confirm that x264 from spec2017 now builds cleanly again.  Still not sure which of the two was the immediate trigger.

https://github.com/llvm/llvm-project/pull/72583