[clang] [Driver][Frontend] Add -f[no-]ms-anonymous-structs flag to control Microsoft anonymous struct/union extension (PR #176551)

[Aaron Ballman via cfe-commits]

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@@ -3327,6 +3327,14 @@ 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]>;
+defm ms_anonymous_structs
+    : BoolFOption<
+          "ms-anonymous-structs", LangOpts<"MSAnonymousStructs">, DefaultFalse,
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AaronBallman wrote:

@jansvoboda11 would it make sense (and is it possible) to change `DefaultFalse` to instead be `ImpliedByAnyOf<[fms_extensions.KeyPath]>` so that when `-fms-extensions` is enable, `-fms-anonymous-structs` is also enabled?

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