Add Dockerfile and script for building WASM files

src/runtime/javascript/build-wasm.sh

@@ -0,0 +1,10 @@
+#! /usr/bin/env bash
+set -e
+cd ../c
+
+# Build inside Docker image
+IMAGE="gf/build-c-runtime-wasm"
+docker build . --file Dockerfile-wasm --tag $IMAGE
+
+# Copy bulit files from container to host
+docker run --rm --volume "$PWD":/tmp/host $IMAGE bash -c "cp pgf.js pgf.wasm /tmp/host/"