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

[Hubert Tong via cfe-commits]

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@@ -7156,8 +7156,10 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
 
   // -fms-extensions=0 is default.
   if (Args.hasFlag(options::OPT_fms_extensions, options::OPT_fno_ms_extensions,
-                   IsWindowsMSVC || IsUEFI))
+                   IsWindowsMSVC || IsUEFI)) {
     CmdArgs.push_back("-fms-extensions");
+    CmdArgs.push_back("-fms-anonymous-structs");
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hubert-reinterpretcast wrote:

@riyaz86a, thanks for confirming in our "offline" discussion that the implication mechanism of `ImpliedByAnyOf` is sufficient. As discussed, please remove the driver and driver test changes. Thanks.

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