[llvm] [APFloat] Add exp function for APFloat::IEEESsingle using expf implementation from LLVM libc. (PR #143959)

[Joseph Huber via llvm-commits]

https://github.com/jhuber6 commented:

Given sparse checkouts, I'm wondering if we should check if `lib/` exists in the tree and use this by default if so.

https://github.com/llvm/llvm-project/pull/143959