Bring back accidentally deleted raytrace build script

examples/raytrace-parallel/build.sh

@@ -0,0 +1,25 @@
+#!/bin/sh
+
+set -ex
+
+# Two critical steps are required here to get this working:
+#
+# * First, the Rust standard library needs to be compiled. The default version
+#   is not compatible with atomics so we need to compile a version, with xargo,
+#   that is compatible.
+#
+# * Next we need to compile everything with the `atomics` feature enabled,
+#   ensuring that LLVM will generate atomic instructions and such.
+RUSTFLAGS='-C target-feature=+atomics' \
+  rustup run nightly xargo build --target wasm32-unknown-unknown --release
+
+# Threading support is disabled by default in wasm-bindgen, so use an env var
+# here to turn it on for our bindings generation. Also note that webpack isn't
+# currently compatible with atomics, so we go with the --no-modules output.
+WASM_BINDGEN_THREADS=1 \
+  cargo run --manifest-path ../../crates/cli/Cargo.toml \
+    --bin wasm-bindgen -- \
+    ../../target/wasm32-unknown-unknown/release/raytrace_parallel.wasm --out-dir . \
+    --no-modules
+
+python3 -m http.server