Fix CI to recurse submodules

Author: nickclark2016

.github/workflows/build-linux.yaml

@@ -15,6 +15,8 @@ jobs:
     steps:
       - name: Checkout
         uses: actions/checkout@v2
+        with:
+          submodules: recursive
       - name: Configure Ubuntu Libraries
         run: sudo apt-get install -y libxcursor-dev libxrandr-dev libxinerama-dev libxi-dev mesa-common-dev
       - name: Configure Clang