Add script to automate WebAssembly builds

[tiran]

Feature or enhancement

I propose to add a tool that automates WebAssembly builds and guides developers through installation process of SDKs.

Pitch

It is not trivial to build Python on WebAssembly platforms. Developers have to install the correct SDKs, active them or set env vars. They also have to build a build Python interpreter before they can compile Python to WASM. Each variant requires wrappers for configure and make and several configure arguments.

I'm going to automate the steps with a Python script. The script features several build profiles and can run tests, too.

  $ ./Tools/wasm/wasm_builder.py emscripten-browser compile
  $ ./Tools/wasm/wasm_builder.py emscripten-node-dl test
  $ ./Tools/wasm/wasm_builder.py wasi test