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

[Hubert Tong via cfe-commits]

================
@@ -8,6 +8,25 @@
 // RUN:   -Wno-pointer-to-int-cast -Wmicrosoft -verify=ms-anonymous -fms-compatibility
 // RUN: %clang_cc1 -triple i686-windows %s -fsyntax-only -Wno-unused-value \
 // RUN:   -Wno-pointer-to-int-cast -Wmicrosoft -verify=ms-anonymous-dis
+// Test that explicit -fno-ms-anonymous-structs does not enable the feature
----------------
hubert-reinterpretcast wrote:

```suggestion
// Test that explicit -fno-ms-anonymous-structs does not enable the feature.
```

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