[llvm] [X86][NVPTX][LegalizeDAG] If i16 legal, legalize FABS/FNEG/FCOPYSIGN (f16) with Expand (PR #106153)

[Simon Pilgrim via llvm-commits]

https://github.com/RKSimon requested changes to this pull request.

please can you rebase? I've already added additional test coverage to fp16-libcalls.ll, including copysign/fabs/fneg etc.

https://github.com/llvm/llvm-project/pull/106153