This test was failing on our downstream (bare-metal) runs and only now I got around to investigate it.
The problem is, this test assumes the Itanium ABI, whereas EHABI requires the exception address to be 8-byte aligned.
I was a bit puzzled at first because this should've failed on the public arm-linux builder too. I think the reason it passes there is because we don't include libunwind headers in the include path when running the libcxxabi tests, so the system unwind.h gets picked up.
I think the correct default here is None, not ../libunwind/src, since we might not be using libunwind at all.