[llvm] SelectionDAG: Use qNaN constant if FCANONICALIZE not LegalOrCustom (PR #104564)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm commented:

What does the expand action even do? We can't implement this in terms of any generic operations. Targets have to handle it somehow 

https://github.com/llvm/llvm-project/pull/104564