[Documentation] non-docker way to build wasm? about ruby.wasm

[kateinoigakukun]

@rkh Thank you for your try:) Just FYI, adding -e "GNUMAKEFLAGS=-j$((1 + $(nproc --all)))" to docker run would speed up the ruby build.

[rkh]

@kateinoigakukun Oh great. FYI running it in Docker works like a charm, not a single hick up, other than it being slow (for us this isn't a deal breaker, can move it to a beefy build system).

@rubyFeedback unless you want to patch Ruby or compile a native extension, you shouldn't need to install Docker at all to build a wasm. Instead follow the wasi-vfs steps in the readme. Significantly faster as well. You can also selectively include the standard library, add your own Ruby files, etc.

[kateinoigakukun]

The build steps for setting up tools are a little bit complicated, so it's recommended to use docker image, but it's optional.
If you want to build outside of the image, you need to install tools and set environment variables correctly following the section: https://github.com/ruby/ruby.wasm#dependencies

Since the step is complicated, I don't want to write it down in a natural language for maintainability. I hope the Dockerfile script and CI configuration would help you to understand the build steps.

[rkh]

Running rake build:head-wasm32-unknown-wasi-full is absurdly slow for me (probably due to virtualization, this is on a MacBook M1 Max). The command has been running for hours (still showing progress). Once I made sure it works I'll try to build without docker and can report back.

[kateinoigakukun]

I've updated the build system to install dependencies automatically on demand, and it's now docker-free. Also added build instructions in CONTRIBUTING.md.

Feel free to re-open this issue if there is something missed.