[clang] [CUDA][Win32] Add `fma(long double,..)` to math forward declares. (PR #73756)

[Artem Belevich via cfe-commits]

Artem-B wrote:

I'm not familiar enough with MSVC. 

@rnk -- what's the best way to check for compilation with microsoft's stardard C++ library?

https://github.com/llvm/llvm-project/pull/73756