web-wasi-emulated-threads: initial addition

Todos:

- Add to CI if possible (builds LLVM/Clang)
- Add to README

web-wasi-emulated-threads/download-build-install-wasi-sdk.sh

@@ -0,0 +1,36 @@
+#!/usr/bin/env bash
+
+set -eox pipefail
+
+mkdir /tmp/dl
+cd /tmp/dl
+
+wasi_sdk_dir=/opt/wasi-sdk
+mkdir -p $wasi_sdk_dir
+
+curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y
+export PATH=$HOME/.cargo/bin:$PATH
+
+git clone --recurse-submodules -b enable-libcxx-threads https://github.com/thewtex/wasi-sdk
+cd wasi-sdk
+git fetch origin --tags
+git remote add upstream https://github.com/WebAssembly/wasi-sdk
+git fetch upstream wasi-sdk-${WASI_VERSION}
+
+./ci/build.sh
+cd build/dist
+tar xzf wasi-toolchain-*.tar.gz --strip-components=1 -C /opt/wasi-sdk
+mkdir -p /opt/wasi-sdk/share/wasi-sysroot
+tar xzf wasi-sysroot-*.tar.gz --strip-components=1 -C /opt/wasi-sdk/share/wasi-sysroot
+for wasi_toolchain in wasi wasip1 wasip2; do
+  libclang_rt_out_dir=/opt/wasi-sdk/lib/clang/${LLVM_VERSION}/${wasi_toolchain}
+  mkdir -p $libclang_rt_out_dir
+  tar xzf ./libclang_rt.builtins-*.tar.gz --strip-components=1 -C $libclang_rt_out_dir
+done
+mkdir -p /opt/wasi-sdk/lib/clang/${LLVM_VERSION}/lib/wasm32-unknown-wasi
+cp ${libclang_rt_out_dir}/libclang_rt.builtins-wasm32.a /opt/wasi-sdk/lib/clang/${LLVM_VERSION}/lib/wasm32-unknown-wasi/libclang_rt.builtins.a
+
+cd /tmp/
+rm -rf /tmp/dl
+rm -rf $HOME/.cargo
+