fixes in setup.py for emscripten-wasm32 build

[DerThorsten]

These changes are needed to build the package with emscripten. This PR disables / bypasses the usage of the cpuinfo package when building for emscripten-wasm32. Furthermore I removed the threading argument from blosc when compiling for emscripten.

TODO:

• [ ] Unit tests and/or doctests in docstrings
• [ ] Tests pass locally
• [ ] Docstrings and API docs for any new/modified user-facing classes and functions
• [ ] Changes documented in docs/release.rst
• [ ] Docs build locally
• [ ] GitHub Actions CI passes
• [ ] Test coverage to 100% (Codecov passes)

[agriyakhetarpal]

See also: #529, which is also a contemporary PR that performs a subset of the changes here. I'm not fully sure how py-cpuinfo is working for the Pyodide builds. :)