[clang] [HLSL] Support packoffset attribute in AST (PR #89836)

[Damyan Pepper via cfe-commits]

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@@ -1745,5 +1745,7 @@ def err_hlsl_separate_attr_arg_and_number : Error<"wrong argument format for hls
 def ext_hlsl_access_specifiers : ExtWarn<
   "access specifiers are a clang HLSL extension">,
   InGroup<HLSLExtension>;
+def err_hlsl_unsupported_component : Error<"invalid component '%0' used; expected 'x', 'y', 'z', or 'w'">;
+def err_hlsl_packoffset_invalid_reg : Error<"invalid resource class specifier '%0' for packoffset, expected 'c'">;
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damyanp wrote:

Should we document that this is an error, while in DXC it is just a warning, in the Clang vs DXC differences page?

https://github.com/llvm/llvm-project/pull/89836