[compiler-rt] [builtins] Avoid using long double in generic sources (PR #69754)

[Pranav Kant via llvm-commits]

pranavk wrote:

Yes, that would make sense to me. *xf pertains to 80 bit float as far as I know.

[Microsoft's long double](https://learn.microsoft.com/en-us/cpp/c-language/type-long-double?view=msvc-170) 

https://github.com/llvm/llvm-project/pull/69754