[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:

> This is a bit of a strange test. None of the other libunwind/libcxxabi tests I've seen do FileCheck on runtime output from the executable. They just rely on carefully placed `assert()`s.

`FileCheck` support for these components was only added earlier this year in d9e52ccd1aeb572f56806bc8f64005afd47dc617 so it is not surprising that tests have not been using it. Also whether or not the unwinder decided to use the VAPI return glue when the VAPI is not active at the time `unw_resume` is called is not possible to inspect directly.

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