[clang] [HLSL] Add validation for the -enable-16bit-types option (PR #85340)

[Chris B via cfe-commits]

================
@@ -753,7 +753,10 @@ def err_drv_hlsl_unsupported_target : Error<
   "HLSL code generation is unsupported for target '%0'">;
 def err_drv_hlsl_bad_shader_required_in_target : Error<
   "%select{shader model|Vulkan environment|shader stage}0 is required as %select{OS|environment}1 in target '%2' for HLSL code generation">;
-
+def err_drv_dxc_enable_16bit_types_option_invalid: Error<
+  "'-enable-16bit-types' option only valid when target shader model [-T] is >= 6.2 and HLSL Version [-HV] is >= hlsl2018, but shader model is '%0' and HLSL Version is '%1'">;
+def err_drv_cc1_hlsl_spirv_fnative_half_type_option_invalid: Error<
+  "'-fnative-half-type' option only valid when HLSL language standard version is >= 2018, but language standard version is '%0'">;
----------------
llvm-beanz wrote:

nit: I think you can use one diagnostic to express all cases. Something like:
```suggestion
def err_drv_hlsl_16bit_types_unsupported: Error<
  "'%0' option requires target HLSL Version >= 2018 and %select{|shader model >= 6.2}1, but HLSL Version is '%2'" %select{|and shader model is '%3'}1>;
```

Then you can emit it like:

```c++
Diags.Report(diag::err_drv_hlsl_16bit_types_unsupported)
                << "-whichever-flag" << T.isDXIL() ? 1 :0 /* 1 if dxil, 0 if spirv */
                << Std.getName() << T.getOSVersion().getAsString(); // For SPIRV you can optionally leave off the last parameter.
```

https://github.com/llvm/llvm-project/pull/85340