[compiler-rt] [builtins] Avoid using long double in FreeBSD standalone environment (PR #76175)

[Alexander Richardson via llvm-commits]

https://github.com/arichardson approved this pull request.

I think the uqwords struct should be hoisted before the `#ifdef` block for the floating point types but otherwise this looks good to me. 

https://github.com/llvm/llvm-project/pull/76175