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

[Farzon Lotfi via cfe-commits]

farzonl 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 tract which intrinsics we have completed for the SPIRV backend.

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