Add Windows CI job (jpsim#282)

Author: jpsim

.github/workflows/swiftpm.yml

@@ -46,3 +46,31 @@ jobs:
       - uses: actions/checkout@v2
       - run: YAMS_DEFAULT_ENCODING=UTF16 swift test --parallel
       - run: YAMS_DEFAULT_ENCODING=UTF8 swift test --parallel
+
+  Windows:
+    runs-on: windows-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: seanmiddleditch/gha-setup-vsdevenv@master
+      - name: Install swift-DEVELOPMENT-SNAPSHOT-2020-10-29-a
+        run: |
+          Install-Binary -Url "https://swift.org/builds/development/windows10/swift-DEVELOPMENT-SNAPSHOT-2020-10-29-a/swift-DEVELOPMENT-SNAPSHOT-2020-10-29-a-windows10.exe" -Name "installer.exe" -ArgumentList ("-q")
+      - name: Set Environment Variables
+        run: |
+          echo "::set-env name=SDKROOT::C:\Library\Developer\Platforms\Windows.platform\Developer\SDKs\Windows.sdk"
+          echo "::set-env name=DEVELOPER_DIR::C:\Library\Developer"
+      - name: Adjust Paths
+        run: |
+          echo "::add-path::C:\Library\Developer\Toolchains\unknown-Asserts-development.xctoolchain\usr\bin;C:\Library\Swift-development\bin;C:\Library\icu-67\usr\bin"
+      - name: Install Supporting Files
+        shell: cmd
+        run: |
+          copy "%SDKROOT%\usr\share\ucrt.modulemap" "%UniversalCRTSdkDir%\Include\%UCRTVersion%\ucrt\module.modulemap"
+          copy "%SDKROOT%\usr\share\visualc.modulemap" "%VCToolsInstallDir%\include\module.modulemap"
+          copy "%SDKROOT%\usr\share\visualc.apinotes" "%VCToolsInstallDir%\include\visualc.apinotes"
+          copy "%SDKROOT%\usr\share\winsdk.modulemap" "%UniversalCRTSdkDir%\Include\%UCRTVersion%\um\module.modulemap"
+      - name: Build
+        run: swift build -v
+      - name: Test
+        # TODO: Run all tests when this test runner crash is fixed: https://bugs.swift.org/browse/SR-13819
+        run: swift test -v --filter testBinary