add separate build action for emscripten Repl.CLI

.github/workflows/build.yml

@@ -83,3 +83,28 @@ jobs:
       with:
         name: coverage
         path: coverage
+
+  web:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v1
+    - name: setup emsdk
+      uses: mymindstorm/setup-emsdk@v9
+      with:
+        version: 1.38.40
+        actions-cache-folder: 'emsdk-cache'
+    - name: verify emsdk
+      run: |
+        emcc -v # verify emscripten installed successfully
+    - name: cmake configure
+      run: |
+        emcmake cmake .
+    - name: build
+      run: |
+        cmake --build . --target Luau.Repl.CLI --config Debug # as seen above but only Repl.CLI.
+    - name: upload-artifacts
+    - uses: actions/upload-artifact@v2
+      with:
+        name: luau-web-artifacts
+        path: docs/assets/luau/
+        if-no-files-found: error