[clang] [Frontend][Sema] Add CC1-only -fms-anonymous-structs to enable Microsoft anonymous struct/union feature (PR #176551)

[Erich Keane via cfe-commits]

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@@ -3327,6 +3327,12 @@ def fms_extensions : Flag<["-"], "fms-extensions">, Group<f_Group>,
   Visibility<[ClangOption, CC1Option, CLOption]>,
   HelpText<"Accept some non-standard constructs supported by the Microsoft compiler">,
   MarshallingInfoFlag<LangOpts<"MicrosoftExt">>, ImpliedByAnyOf<[fms_compatibility.KeyPath]>;
+def fms_anonymous_structs
+    : Flag<["-"], "fms-anonymous-structs">,
+      Visibility<[CC1Option]>,
+      MarshallingInfoFlag<LangOpts<"MSAnonymousStructs">>,
+      ImpliedByAnyOf<[fms_extensions.KeyPath, fms_compatibility.KeyPath]>,
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erichkeane wrote:

Are both of these necessary?  I would expect this to cascade from compatibility -> extensions -> here? 

https://github.com/llvm/llvm-project/pull/176551