CI: use test llvm-mingw toolchain

Author: jeremyd2019

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

@@ -266,9 +266,18 @@ jobs:
       - name: Install llvm-mingw
         if: ${{ matrix.mingw == true }}
         run: |
-          curl -LO https://github.com/mstorsjo/llvm-mingw/releases/download/20250114/llvm-mingw-20250114-ucrt-x86_64.zip
+          ARTIFACT_URL=https://github.com/jeremyd2019/llvm-mingw/actions/runs/15080594305/artifacts/3143907630
+          case "$ARTIFACT_URL" in
+          https://github.com/*/actions/runs/[0-9]*/artifacts/[0-9]*)
+            ARTIFACT_URL="$(echo "$ARTIFACT_URL" |
+              sed 's|^\(https://\)\(github.com/\)\(.*/actions/\)runs/[0-9]*/\(artifacts/[0-9]*\)$|\1api.\2repos/\3\4/zip|')"
+              ;;
+          esac
+          curl -H "Authorization: token ${{secrets.GITHUB_TOKEN}}" \
+              -fLo artifact.zip "$ARTIFACT_URL"
+          powershell Expand-Archive artifact.zip -DestinationPath .
           powershell Expand-Archive llvm-mingw*.zip -DestinationPath .
-          del llvm-mingw*.zip
+          del llvm-mingw*.zip artifact.zip
           mv llvm-mingw* c:\llvm-mingw
           echo "c:\llvm-mingw\bin" | Out-File -FilePath $Env:GITHUB_PATH -Encoding utf8 -Append
       - name: Simulate a from-scratch build of llvm-mingw