[llvm] [ConstantFold] Fold `log1p` and `log1pf` when the input parameter is a constant value. (PR #112113)

[Hubert Tong via llvm-commits]

hubert-reinterpretcast wrote:

The negative zero behaviour is optional. Clang on AIX defines neither `__STDC_IEC_559__` nor `__STDC_IEC_60559_BFP__`.

https://github.com/llvm/llvm-project/pull/112113