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

[Tamalampudi Siva Harsha Vardhan Reddy via llvm-commits]

harsha08-2k6 wrote:

**This PR was not generated using AI.** All code, tests, and changes were written manually without the use of AI tools.

I have read and followed the requirements specified in the [Testing libc++ documentation](https://libcxx.llvm.org/TestingLibcxx.html). Specifically:

- The test follows the proper structure with `main(int, char**)` returning 0
- The test file is named `assert.copy_file.pass.cpp` following the naming convention for regression tests
- The test is located in the appropriate directory structure under `libcxx/test/libcxx/`
- The test uses appropriate assertions and validates the fix for the infinite loop issue (#169261)
- The test includes proper header dependencies and follows libc++ testing conventions

If there are any specific requirements from the documentation that need further attention or adjustment, please let me know and I will address them promptly.

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