[llvm] [libc] Revert "[libc][NFC] Refactor FPBits and remove LongDoubleBits specialization (#78192)" (PR #78329)

[Nick Desaulniers via llvm-commits]

nickdesaulniers wrote:

https://lab.llvm.org/buildbot/#/builders/98/builds/31617 the fuchsia build bot is also broken for 32b arm

https://github.com/llvm/llvm-project/pull/78329