update bazel workspace for emscripten 2.0.3 (#613)

* update bazel workspace for emscripten 2.0.3

* test to make sure WORKSPACE is up to date

* make it clear what happened when WORKSPACE is out of date

* intentionally add error to make sure circleci fails properly

* revert intentionally bad commit

* increase visibility of failure message

Co-authored-by: Mitch Foley <mitchfoley@google.com>

scripts/test_bazel.sh

@@ -5,5 +5,20 @@ echo "test bazel"
 set -x
 set -e
 
+# Get the latest version number from emscripten-releases-tag.txt.
+VER=$(grep -oP '(?<=latest\": \")([\d\.]+)(?=\")' \
+        emscripten-releases-tags.txt \
+      | sed --expression "s/\./\\\./g")
+# Based on the latest version number, get the commit hash for that version.
+HASH=$(grep "${VER}" emscripten-releases-tags.txt \
+      | grep -v latest \
+      | cut -f4 -d\")
+      
+FAILMSG="!!! scripts/update_bazel_toolchain.sh needs to be run !!!"
+
+# Ensure the WORKSPACE file is up to date with the latest version.
+grep ${VER} bazel/WORKSPACE || (echo ${FAILMSG} && false)
+grep ${HASH} bazel/WORKSPACE || (echo ${FAILMSG} && false)
+
 cd bazel
 bazel build //hello-world:hello-world-wasm