[clang] [Clang] Add float type support to __builtin_reduce_add and __builtin_reduce_multipy (PR #120367)

[Farzon Lotfi via cfe-commits]

farzonl wrote:

> fp reductions are a nightmare - every time I thought we were getting somewhere, something else fastmath related causes more headaches.

@RKSimon should I not proceed with this PR? I was really hoping to use this in HLSL as it makes implementing many of our runtime apis easy in the frontend.

https://github.com/llvm/llvm-project/pull/120367