[clang] [llvm] [hlsl][dxil][spirv] Add `fma` function (PR #185304)

[Farzon Lotfi via llvm-commits]

================
@@ -4124,6 +4033,8 @@ bool SPIRVInstructionSelector::selectIntrinsic(Register ResVReg,
     return selectAll(ResVReg, ResType, I);
   case Intrinsic::spv_any:
     return selectAny(ResVReg, ResType, I);
+  case Intrinsic::spv_fma:
+    return selectExtInst(ResVReg, ResType, I, CL::fma, GL::Fma);
----------------
farzonl wrote:

wait why do we need an intrinsic for this in spirv when we have `G_FMA`.
```
case TargetOpcode::G_FMA: {
...
llvm/lib/Target/SPIRV/SPIRVInstructionSelector.cpp:1024:    return selectExtInst(ResVReg, ResType, I, CL::fma, GL::Fma);
...
}
```

https://github.com/llvm/llvm-project/pull/185304