[SPIRV][HLSL] Add mad intrinsic lowering for spirv (#89130)

- `clang/lib/CodeGen/CGBuiltin.cpp` - Add a generic mull add
implementation. Make DXIL implementation tied to target.

resolves #88944

GitOrigin-RevId: 5a1a5226b578ec7f123f67efd4e24e39fecd11d7
2 files changed