Enable macOS and Windows CI builds

These will most likely break

.github/workflows/ci.yml

@@ -1,20 +1,32 @@
 name: CI
 on: [push]
 jobs:
-    linux:
+    job:
-        runs-on: ubuntu-latest
+      name: ${{ matrix.os }}-${{ github.workflow }}
-        env:
+      runs-on: ${{ matrix.os }}
-            CC: gcc-9
+      strategy:
-            CXX: g++-9
+        fail-fast: false
+        matrix:
+          os: [ ubuntu-latest, macos-latest, windows-latest ]
+          include:
+            - os: windows-latest
+              triplet: x64-windows
+            - os: ubuntu-latest
+              triplet: x64-linux
+            - os: macos-latest
+              triplet: x64-osx
       steps:
       - uses: actions/checkout@v2
       - name: Download LunarG key
         run: wget -qO - https://packages.lunarg.com/lunarg-signing-key-pub.asc | sudo apt-key add -
       - name: Add LunarG Vulkan repository
+        if: matrix.os == 'ubuntu-latest'
         run: sudo wget -qO /etc/apt/sources.list.d/lunarg-vulkan-bionic.list https://packages.lunarg.com/vulkan/lunarg-vulkan-bionic.list
       - name: Update package list
+        if: matrix.os == 'ubuntu-latest'
         run: sudo apt update
       - name: Install Vulkan SDK
+        if: matrix.os == 'ubuntu-latest'
         run: sudo apt install -f vulkan-sdk libsdl2-dev
       - name: Configure
         run: cmake -S. -Bbuild -DCMAKE_BUILD_TYPE=Release