[clang] [clang][Sema][Tests] Add test coverage for function-like macro diagnostic edge cases and C++ (PR #223895)

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

Landing despite precommit CI coming back red, the build failures appear to be unrelated:

>      File "/home/gha/actions-runner/_work/llvm-project/llvm-project/lldb/test/API/lang/objc/synthesized-property-accessor/TestSynthesizedPropertyAccessor.py", line 11, in TestSynthesizedPropertyAccessor
>      @skipIf(compiler="clang", compiler_version=["<", "22.0"])
>       ^^^^^^
>  NameError: name 'skipIf' is not defined

and

>   requests.exceptions.ConnectionError: HTTPConnectionPool(host='premerge-advisor.premerge-advisor.svc.cluster.local', port=5000): Max retries exceeded with url: /explain (Caused by NewConnectionError("HTTPConnection(host='premerge-advisor.premerge-advisor.svc.cluster.local', port=5000): Failed to establish a new connection: [Errno 111] Connection refused"))


https://github.com/llvm/llvm-project/pull/223895