ci: add Windows builds

Add automated Windows builds.

Use curl-for-win with llvm + mingw64, and a minimal curl build with no
external dependencies to build x64, ARM64 and x86 `trurl.exe`.

Boost build performance by not building the curl tool [EXPERIMENTAL].
Use a customized curl-for-win build with disabled TLS to further reduce
footprint and build time.

Non-UNITY libcurl builds can make turl binaries about 120KB smaller, but
they require 2x build times (4m vs. 2m), so opted not to use those here.

Ref: curl#109
Closes curl#249

.github/workflows/curl-for-win.yml

@@ -0,0 +1,55 @@
+# Copyright (C) Viktor Szakats. See LICENSE.md
+# SPDX-License-Identifier: curl
+---
+name: curl-for-win
+
+on:
+  push:
+    branches: ["master"]
+  pull_request:
+    branches: ["master"]
+
+permissions: {}
+
+env:
+  CW_GET: 'curl'
+  CW_MAP: '0'
+  CW_JOBS: '3'
+  CW_PKG_NODELETE: '1'
+  CW_PKG_FLATTEN: '1'
+  DOCKER_CONTENT_TRUST: '1'
+
+jobs:
+  win-llvm:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          path: 'trurl'
+          fetch-depth: 8
+      - name: 'build'
+        env:
+          CW_LLVM_MINGW_DL: '1'
+          CW_LLVM_MINGW_ONLY: '0'
+        run: |
+          git clone --depth 1 https://github.com/curl/curl-for-win
+          mv curl-for-win/* .
+          export CW_CONFIG='-dev-zero-osnotls-nocurltool-win'
+          export CW_REVISION='${{ github.sha }}'
+          . ./_versions.sh
+          docker trust inspect --pretty "${DOCKER_IMAGE}"
+          time docker pull "${DOCKER_IMAGE}"
+          docker images --digests
+          time docker run --volume "$(pwd):$(pwd)" --workdir "$(pwd)" \
+            --env-file <(env | grep -a -E \
+              '^(CW_|GITHUB_)') \
+            "${DOCKER_IMAGE}" \
+            sh -c ./_ci-linux-debian.sh
+
+      - name: 'list dependencies'
+        run: cat urls.txt
+      - uses: actions/upload-artifact@v3
+        with:
+          name: 'trurl-windows'
+          retention-days: 5
+          path: curl-*-*-*/trurl*