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

[via cfe-commits]

github-actions[bot] wrote:

<!--PREMERGE ADVISOR COMMENT: Linux-->
# :penguin: Linux x64 Test Results

* 85462 tests passed
* 1213 tests skipped
* 1 test failed

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

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

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

/home/gha/actions-runner/_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: { 0x38dde930 pointing to "-fsyntax-only", 0x38dde93e pointing to "-x", 0x38dde941 pointing to "c", 0x38dde943 pointing to "clang", 0x38dde949 pointing to "-triple", 0x38dde951 pointing to "x86_64-unknown-linux-gnu", 0x38dde96a pointing to "-std=gnu17", 0x38dde975 pointing to "-fms-extensions", 0x38dde985 pointing to "-fno-convergent-functions", 0x38dde99f pointing to "-ffp-contract=off", 0x38dde9b1 pointing to "-fno-experimental-relative-c++-abi-vtables", 0x38dde9dc pointing to "-fno-file-reproducible", 0x38dde9f3 pointing to "-O0", 0x38dde9f7 pointing to "-fno-loop-interchange", 0x38ddea0d pointing to "-save-temps=obj", 0x38ddea1d pointing to "-fdiagnostics-hotness-threshold=0", 0x38ddea3f 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