[libc++] Use GitHub-provided runners for the windows CI

Author: philnik777

.github/workflows/libcxx-build-and-test.yaml

@@ -199,3 +199,18 @@ jobs:
             **/CMakeError.log
             **/CMakeOutput.log
             **/crash_diagnostics/*
+  windows:
+    runs-on: windows-2019
+    steps:
+      - uses: actions/checkout@v4
+      - name: Install dependencies
+        run: |
+          choco install -y ninja wget
+          wget https://github.com/mstorsjo/llvm-mingw/releases/download/20231128/llvm-mingw-20231128-ucrt-x86_64.zip -O llvm-mingw.zip
+          powershell Expand-Archive llvm-mingw.zip -DestinationPath .
+          del llvm-mingw.zip
+          ren llvm-mingw-20231128-ucrt-x86_64 llvm-mingw
+      - name: clang-cl (DLL)
+        run: |
+          cmd /k echo %path%
+          bash PATH="$PATH:c/Program Files/Git/usr/bin:c/llvm-mingw/bin:c/Program Files (x86)/Microsoft Visual Studio/2019/Enterprise/Common7/IDE/:c/Program Files (x86)/Microsoft Visual Studio/2019/Enterprise/Common7/IDE/CommonExt ensions/Microsoft/TeamFoundation/Team Explorer:c/Program Files (x86)/Microsoft Visual Studio/2019/Enterprise/Common7/IDE/CommonExtensions/Microsoft/CMake/CMake/bin:c/Program Files (x86)/Microsoft Visual Studio/2019/Enterprise/Common7/IDE/CommonExtensions/Microsoft/CMake/Ninja:c/Program Files (x86)/Microsoft Visual Studio/2019/Enterprise/Common7/IDE/CommonExtensions/Microsoft/TeamFoundation/Team Explorer:c/Program Files (x86)/Microsoft Visual Studio/2019/Enterprise/Common7/IDE/CommonExtensions/Microsoft/TestWindow:c/Program Files (x86)/Microsoft Visual Studio/2019/Enterprise/Common7/IDE/VC/VCPackages:c/Program Files (x86)/Microsoft Visual Studio/2019/Enterprise/Common7/Tools/:c/Program Files (x86)/Microsoft Visual Studio/2019/Enterprise/Common7/Tools/devinit:c/Program Files (x86)/Microsoft Visual Studio/2019/Enterprise/MSBuild/Current/Bin:c/Program Files (x86)/Microsoft Visual Studio/2019/Enterprise/MSBuild/Current/bin/Roslyn:c/Program Files (x86)/Microsoft Visual Studio/2019/Enterprise/VC/Tools/MSVC/14.29.30133/bin/HostX64/x64:c/Program Files (x86)/Microsoft SDKs/Windows/v10.0A/bin/NETFX 4.8 Tools/x64/:c/Program Files (x86)/Windows Kits/10/bin/10.0.19041.0/x64:c/Program Files (x86)/Windows Kits/10/bin/x64:c/Windows/Microsoft.NET/Framework64/v4.0.30319" libcxx/utils/ci/run-buildbot clang-cl-dll