Add mingw target for static builds

Author: mulimoen

.github/workflows/ci.yml

@@ -170,14 +170,18 @@ jobs:
       fail-fast: false
       matrix:
         rust: [stable]
-        version: ["1.8", "1.10", "1.12"]
+        include:
+          - {target: "x64_64-pc-windows-msvc", version: "1.8"}
+          - {target: "x64_64-pc-windows-msvc", version: "1.10"}
+          - {target: "x64_64-pc-windows-msvc", version: "1.12"}
+          - {target: "x64_64-pc-windows-gnu", version: "1.12"}
     steps:
       - name: Checkout repository
         uses: actions/checkout@v2
         with: {submodules: true}
       - name: Install Rust (${{matrix.rust}})
         uses: actions-rs/toolchain@v1
-        with: {toolchain: '${{matrix.rust}}', profile: minimal, override: true}
+        with: {toolchain: '${{matrix.rust}}', target: "${{matrix.target}}", profile: minimal, override: true}
       - name: Configure environment
         shell: bash
         run: |