[libunwind] [libunwind][test][AIX] Add C API test for unwinding from AIX VAPI (non-signal-handler case) (PR #209306)

[Hubert Tong via cfe-commits]

hubert-reinterpretcast wrote:

The failure in [windows (clang-cl-static-crt, false, clang-cl, clang-cl)](https://github.com/llvm/llvm-project/actions/runs/29384370246/job/87261796844?pr=209306#logs) on `llvm-libc++-static-clangcl.cfg.in :: std/thread/thread.mutex/thread.mutex.requirements/thread.sharedtimedmutex.requirements/thread.sharedtimedmutex.class/try_lock_shared_until.pass.cpp` clearly has nothing to do with this PR.

https://github.com/llvm/llvm-project/pull/209306