[llvm] [SelectionDAG] Propogate Disjoint flag. (PR #88370)

[via llvm-commits]

goldsteinn wrote:

> Tests?

Just a note, the general practice is to "pre commit" your tests. What that means is your PR should have two commits.
Commit 1) Tests w/o your implementation
Commit 2) Your implementation w/ updated tests (using `llvm/utils/update_llc_test_checks.py` in this case).

That way we can see the diff.

https://github.com/llvm/llvm-project/pull/88370