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

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github-actions[bot] wrote:

<!--PREMERGE ADVISOR COMMENT: Windows-->
# :window: Windows x64 Test Results

* 51862 tests passed
* 908 tests skipped
* 1 test failed

## Failed Tests
(click on a test name to see its output)

### Clang-Unit
<details>
<summary>Clang-Unit._/AllClangUnitTests_exe/CommandLineTest/MSAnonymousStructsEnabledByMSExtensions</summary>

```
Script:
--
C:\_work\llvm-project\llvm-project\build\tools\clang\unittests\.\AllClangUnitTests.exe --gtest_filter=CommandLineTest.MSAnonymousStructsEnabledByMSExtensions
--
C:\_work\llvm-project\llvm-project\clang\unittests\Frontend\CompilerInvocationTest.cpp:210
Value of: Invocation.getLangOpts().MSAnonymousStructs
  Actual: false
Expected: true

C:\_work\llvm-project\llvm-project\clang\unittests\Frontend\CompilerInvocationTest.cpp:214
Value of: GeneratedArgs
Expected: contains at least one element that is equal to "-fms-anonymous-structs"
  Actual: { 0000023E9AA586B8 pointing to "-fsyntax-only", 0000023E9AA586C6 pointing to "-x", 0000023E9AA586C9 pointing to "c", 0000023E9AA586CB pointing to "clang", 0000023E9AA586D1 pointing to "-triple", 0000023E9AA586D9 pointing to "x86_64-pc-windows-msvc", 0000023E9AA586F0 pointing to "-std=gnu17", 0000023E9AA586FB pointing to "-fms-extensions", 0000023E9AA5870B pointing to "-fno-convergent-functions", 0000023E9AA58725 pointing to "-ffp-contract=off", 0000023E9AA58737 pointing to "-fno-experimental-relative-c++-abi-vtables", 0000023E9AA58762 pointing to "-fno-file-reproducible", 0000023E9AA58779 pointing to "-O0", 0000023E9AA5877D pointing to "-fno-loop-interchange", 0000023E9AA58793 pointing to "-save-temps=obj", 0000023E9AA587A3 pointing to "-fdiagnostics-hotness-threshold=0", 0000023E9AA587C5 pointing to "-fdiagnostics-misexpect-tolerance=0" }


```
</details>

If these failures are unrelated to your changes (for example tests are broken or flaky at HEAD), please open an issue at https://github.com/llvm/llvm-project/issues and add the `infrastructure` label.

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