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. :)