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

[Simon Pilgrim via llvm-commits]

RKSimon wrote:

@pawan-nirpal-031 Can we just mul * 1.0 as the default expansion for ISD::FCANONICALIZE, adding a TargetLowering::expandFCANONICALIZE method?

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