[llvm] [SDAG] Handle extract_subvector in isKnownNeverNaN (PR #131581)

[Philip Reames via llvm-commits]

https://github.com/preames approved this pull request.

LGTM

Might be worth checking, do we get the insert subvector into undef vector case?

https://github.com/llvm/llvm-project/pull/131581