[clang] Adds a pseudonym to clang"s windows mangler... (PR #97792)

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memory-thrasher wrote:

ya it's something with my local build env. same test is now failing when built from the commit before mine. Looks like they passed on the build server though so this should be ready. I fixed the things you mentioned @bolshakov-a . Let me know if you have a different phrasing for those diagnositcs in mind or if you want any other changes made.

https://github.com/llvm/llvm-project/pull/97792