Max Desiatov

With changes I've pushed the build is now successful with latest development snapshots when building `NIOCore` and `NIOHTTP1` targets for single-threaded WASI.

Pushed more changes so that it uses `wasi_pthread` when multi-threading is available with `wasm32-unknown-wasip1-threads` triples.

> w.r.t. disabling locks on WASI: Honestly I think this can go in as is: Today this is fine and if threading really happens this will blow up very obviously...

What's the output of `swift --version` after setting `TOOLCHAINS` this way? I suspect the value of `TOOLCHAINS` is wrong, I've never seen it set in this format. IIUC the top-level...

This has been merged to LLVM as [`R_WASM_MEMORY_ADDR_LOCREL_I32`](https://github.com/llvm/llvm-project/blob/1049735d0739acf01ebf8f1208cb28efc0365658/lld/wasm/InputChunks.cpp#L152). Does this mean that the functionality is fully implemented now? Do we need to submit a PR here clarifying how it works,...

Can this PR also be submitted to the upstream LLVM repository?

> Presumably this is generating the wrong result (I think it probably returns `aarch64-unknown-linux-gnu`), and I assume that the `Triples` arrays are in part an attempt to work around that...

@swift-ci test webassembly

I think lowering the requirement to 5.8 should be possible, I will look into that.

@swift-ci test WebAssembly