github: Run test-toolchain using busybox rather than msys2

.github/workflows/build.yml

@@ -454,9 +454,6 @@ jobs:
   # Run llvm-mingw's tests with the cross-built toolchains from above.
   test-toolchain:
     needs: [linux-cross-windows]
-    defaults:
-      run:
-        shell: msys2 {0}
     strategy:
       fail-fast: false
       matrix:
@@ -466,26 +463,23 @@ jobs:
           - aarch64
     runs-on: ${{startsWith(matrix.arch, 'a') && 'windows-11-arm' || 'windows-latest'}}
     steps:
-      - uses: msys2/setup-msys2@v2
-        with:
-          msystem: msys
-          install: >-
-            unzip
-            make
       - uses: actions/download-artifact@v4
         with:
           name: windows-ucrt-${{matrix.arch}}-toolchain
       - name: Unpack toolchain
         run: |
-          unzip -q llvm-mingw-*.zip
-          rm llvm-mingw-*.zip
-          mv llvm-mingw-* /llvm-mingw
+          Expand-Archive llvm-mingw-*.zip -DestinationPath .
+          del llvm-mingw-*.zip
+          mv llvm-mingw-* c:\llvm-mingw
+          echo "c:\llvm-mingw\busybox\bin" | Out-File -FilePath $Env:GITHUB_PATH -Encoding utf8 -Append
+          echo "c:\llvm-mingw\bin" | Out-File -FilePath $Env:GITHUB_PATH -Encoding utf8 -Append
       - uses: actions/checkout@v4
       - name: Run tests
+        shell: sh
         run: |
-          ./test-libcxx-module.sh /llvm-mingw
-          ./run-tests.sh /llvm-mingw
-          ./run-lldb-tests.sh /llvm-mingw
+          ./test-libcxx-module.sh c:/llvm-mingw
+          ./run-tests.sh c:/llvm-mingw
+          ./run-lldb-tests.sh c:/llvm-mingw
 
   # Run libcxx's tests with the cross-built toolchains from above.
   # (This builds its own copy of libcxx, but it should be pretty much