Added basic support for wasm32-emscripten target

[permutationlock]

Inspired by #10836, these additions allow Zig objects and libraries built with the wasm32-emscripten target to link libc and use the std.os interface. These files may then be linked into an Emscripten web app with emcc.

I realize that #10836 is not approved, but I thought that I would at least put this out there. I have used Zig with Emscripten successfully via this patch in a few personal projects (e.g. a work-in-progress websocket/tcp game server or a toy test of threads).

I also realize that Emscripten has a lot of idiosyncracies, and I have only accounted for what I've encountered (e.g. Emscripten libc exports getentropy but not getrandom).

[jedisct1]

This is nice!

But from a practical perspective, how can the output be used without the relevant Javascript bits?

[permutationlock]

But from a practical perspective, how can the output be used without the relevant Javascript bits?

Yes, this target is only useful when using emcc as a linker which generates the corresponding JavaScript bindings. Unless I misunderstood the question?

[jedisct1]

Got it, so the emscripten toolchain is still required.

But being able to write code in Zig that can run in browsers (beyond wasm32-freestanding which is very limited) is very cool.

[permutationlock]

It would be nice to have a wasm browser option that doesn't depend on Emscripten, but as far as I know there aren't any great alternatives other than binding everything yourself. There was some interesting discussion in the recent WASIX issue #17115.

[permutationlock]

I see that a check is failing, but the error says that the Ninja build system is not found. Is this an issue that I need to fix with my PR or is something else going on?

Also @jedisct1 I just noticed who you are, I use libsodium a lot and it's awesome!

[jedisct1]

Don't worry, the ninja error is not related to your changes.

[andrewrk]

Thanks!