[libcxx-commits] [libcxx] [libc++][test] Workaround for atomic tests linker errors on Linux systems without libatomic.so (PR #73398)

[Louis Dionne via libcxx-commits]

https://github.com/ldionne approved this pull request.

I see this in https://buildkite.com/llvm-project/libcxx-ci/builds/31901#018c15d9-3491-4b6f-b2d5-92ce78d2c7a9

```
Unexpectedly Passed Tests (17):
  libcxx/atomics/atomics.types.generic/atomics.types.float/lockfree.pass.cpp
  std/atomics/atomics.types.generic/atomics.types.float/assign.pass.cpp
  std/atomics/atomics.types.generic/atomics.types.float/compare_exchange_strong.pass.cpp
  std/atomics/atomics.types.generic/atomics.types.float/compare_exchange_weak.pass.cpp
  std/atomics/atomics.types.generic/atomics.types.float/ctor.pass.cpp
  std/atomics/atomics.types.generic/atomics.types.float/exchange.pass.cpp
  std/atomics/atomics.types.generic/atomics.types.float/fetch_add.pass.cpp
  std/atomics/atomics.types.generic/atomics.types.float/fetch_sub.pass.cpp
  std/atomics/atomics.types.generic/atomics.types.float/load.pass.cpp
  std/atomics/atomics.types.generic/atomics.types.float/lockfree.pass.cpp
  std/atomics/atomics.types.generic/atomics.types.float/notify_all.pass.cpp
  std/atomics/atomics.types.generic/atomics.types.float/notify_one.pass.cpp
  std/atomics/atomics.types.generic/atomics.types.float/operator.float.pass.cpp
  std/atomics/atomics.types.generic/atomics.types.float/operator.minus_equals.pass.cpp
  std/atomics/atomics.types.generic/atomics.types.float/operator.plus_equals.pass.cpp
  std/atomics/atomics.types.generic/atomics.types.float/store.pass.cpp
  std/atomics/atomics.types.generic/atomics.types.float/wait.pass.cpp
```

I think it means that we're failing to detect `non-lockfree-atomics` on Windows, yet the code apparently seems to work. To unblock this patch and restore some CI stability, we could mark these tests as `UNSUPPORTED: !non-lockfree-atomics` and investigate the Windows problems separately. I suspect it would be really easy for @mstorsjo to help us out here.

https://github.com/llvm/llvm-project/pull/73398