The "Python bindings (Pyodide)" CI job fails at CMake configure time
because Emscripten's cross-compiler cannot pass the `std::atomic` link
tests in `check_link_atomic.cmake`, resulting in a fatal error even
though Pyodide builds are single-threaded and never need `libatomic`.
## Change
- **`cmake/check_link_atomic.cmake`**: guard the entire atomic check
behind `if (NOT (EMSCRIPTEN OR Z3_SINGLE_THREADED))`. Emscripten sets
`EMSCRIPTEN` automatically via `emcmake`; Pyodide builds also pass
`-DZ3_SINGLE_THREADED=TRUE`, so either condition is sufficient to bypass
the check safely.
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Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
