[llvm] [libc] [libc] Move printf long double to simple calc (PR #75414)

[via llvm-commits]

https://github.com/michaelrj-google commented:

I see what you mean about this being a rather complex patch, I've addressed the simple comments and will update this patch again when I have an easier-to-read design.

https://github.com/llvm/llvm-project/pull/75414