[clang] [HLSL] Implementation of the fmod intrinsic (PR #108849)

[Zhengxing li via cfe-commits]

lizhengxing wrote:

> The SPIRV frem testing doesn't appear to be complete in `llvm/test/CodeGen/SPIRV/instructions/scalar-floating-point-arithmetic.ll` `llvm/test/CodeGen/SPIRV/instructions/vector-floating-point-arithmetic.ll`
> 
> for all our cases we defined in `hlsl_intrinsics.h`. Should we add more test cases?
> 
> Personally I'd like to see at least one test case in: `llvm/test/CodeGen/SPIRV/hlsl-intrinsics/fmod.ll` Makes it easy to track which intrinsics we have completed for the SPIRV backend.

I'll add those codegen tests in the second PR for #99118 .  That PR is backend specific.

https://github.com/llvm/llvm-project/pull/108849