[llvm] Add regression test for libcxx copy_file infinite loop issue (#169261) (PR #169288)

[Yanzuo Liu via llvm-commits]

zwuis wrote:

If AI was used to create PR, please disclose it. And to what extent it was used.

Please read https://libcxx.llvm.org/TestingLibcxx.html and follow the requirement in the document.

https://github.com/llvm/llvm-project/pull/169288