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

[Farzon Lotfi via cfe-commits]

farzonl wrote:

This LGTM. There is one last thing we might want to do. But I'm not requiring it for sign off.
We ussually add elementwise math builtins here:
- `clang/test/CodeGen/builtins-elementwise-math.c`
-`clang/test/CodeGen/strictfp-elementwise-bulitins.cpp`
- `clang/test/Sema/builtins-elementwise-math.c`
- `clang/test/SemaCXX/builtins-elementwise-math.cpp`

Also I'd take a look at the existing fmod test cases and make sure there is nothing we need to update there:
```bash
clang/test/CodeGen/X86/math-builtins.c:11:  f = __builtin_fmod(f,f);    f = __builtin_fmodf(f,f);   f =  __builtin_fmodl(f,f);  f = __builtin_fmodf128(f,f);
clang/test/CodeGen/builtins.c:318:  resd = __builtin_fmod(D,D);
clang/test/CodeGen/constrained-math-builtins.c:11:  f = __builtin_fmod(f,f);    f = __builtin_fmodf(f,f);   f =  __builtin_fmodl(f,f); f = __builtin_fmodf128(f,f);
clang/test/CodeGenOpenCL/builtins-f16.cl:55:  res = __builtin_fmodf16(h0, h1);
```







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