[llvm] [PowerPC] improve performance on the isNan and !isNan function in case of -ffp-model=strict" (PR #215587)

[zhijian lin via llvm-commits]

diggerlin wrote:

> I don't think there's any point in doing this. This IR is not canonical. instcombine turns all of your test functions into fcmp ord/uno as-is

I implement customer lower in the PPCTargetLowering::LowerIS_FPCLASS

https://github.com/llvm/llvm-project/pull/215587