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

[Riyaz Ahmad via cfe-commits]

================
@@ -0,0 +1,99 @@
+// RUN: %clang_cc1 -triple i686-windows %s -fsyntax-only -Wno-unused-value \
+// RUN: -Wno-pointer-to-int-cast -Wmicrosoft -verify=ms-anonymous -fms-anonymous-structs
+// RUN: %clang_cc1 -triple powerpc-ibm-aix %s -fsyntax-only -Wno-unused-value \
+// RUN: -Wno-pointer-to-int-cast -Wmicrosoft -verify=ms-anonymous -fms-anonymous-structs
+// RUN: %clang_cc1 -triple i686-windows %s -fsyntax-only -Wno-unused-value \
+// RUN: -Wno-pointer-to-int-cast -Wmicrosoft -verify=ms-anonymous -fms-extensions
+// RUN: %clang_cc1 -triple i686-windows %s -fsyntax-only -Wno-unused-value \
+// 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
+
+typedef struct notnested {
+  long bad1;
+  long bad2;
+} NOTNESTED;
+
+
+typedef struct nested1 {
+  long a;
+  struct notnested var1;
+  NOTNESTED var2;
----------------
riyaz86a wrote:

I have reduced the test as per suggestion.
1. Simple MS anonymous structure case.
2. Simple MS anonymous union case.
3. One transitive case.
4. Access failure to anonymous structure member when Microsoft extension disabled (-fms-anonymous-structs or -fms-extensions).

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