[llvm] [Support][KnownFPClass] Refine fdiv and fdiv_self class propagation + some minor fixes for propagateXorSign (PR #215014)

[Max Graey via llvm-commits]

MaxGraey wrote:

@dtcxzyw Thanks. Miscompile exactly relate to partial and additional fix for `propagateXorSign` and `positive-zero,positive-zero` subnormal mode. I'll try to fix this in a more proper way

https://github.com/llvm/llvm-project/pull/215014