[llvm] [libc] [libc][NFC] Refactor FPBits and remove LongDoubleBits specialization (PR #78192)

[Nick Desaulniers via llvm-commits]

nickdesaulniers wrote:

ah, sorry, I had the arm32 build bot offline this past week trying to resolve the last of the -Werror issues there (finally fixed by https://github.com/llvm/llvm-project/commit/f1f1875c18b8ba794a073e924b5c61f0ff7ae60b).  Though it seems that this change breaks the build for 32b arm preventing me from re-enabling the build bot.  (I've pinged you on chat most of the error logs, can repost them here if needed). PTAL

https://github.com/llvm/llvm-project/pull/78192