Add GitHub Action to test if project is buildable.

.github/workflows/debug.yml

@@ -0,0 +1,32 @@
+
+name: Check if Cog buildable
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+    branches:
+      - master
+
+jobs:
+  build:
+    name: Build Cog for Intel
+    runs-on: macos-latest
+    steps:
+      - name: Check out repository
+        uses: actions/checkout@v2
+        with:
+          submodules: recursive
+      - name: Run xcodebuild
+        run: >
+          xcodebuild
+            -workspace Cog.xcodeproj/project.xcworkspace
+            -scheme Cog
+            -configuration Debug
+            -derivedDataPath output
+            build
+      - name: Upload Artifact
+        uses: actions/upload-artifact@v2
+        with:
+          name: Cog
+          path: output/Build/Products/Debug/Cog.app