Run the SFTP regression tests on Windows under MSYS2

tests/regress.c holds the only coverage for the Windows SFTP open path,
including TestSftpWindowsOpenFlagMatrix, which walks the RecvOpen
CREAT/EXCL/TRUNC/APPEND matrix against the CreateFile() disposition
table. That test is guarded by USE_WINDOWS_API and ran in no CI job. The
MSVC solution in ide/winvs has no regress project, and regress.c does not
build with cl because it includes arpa/inet.h and unistd.h, so the
disposition fix it locks down could regress unnoticed.

Add an MSYS2 MinGW64 job to the Windows workflow. MinGW defines _WIN32,
so wolfssh/settings.h turns on USE_WINDOWS_API and the Windows-only
branches compile and run. The job builds wolfSSL static, configures
wolfSSH with --enable-sftp, and runs tests/regress.test and
tests/unit.test. wolfsshd is left out: its autotools path is not
MinGW-clean and the MSVC solution already covers it.

.github/workflows/windows-check.yml

@@ -220,3 +220,71 @@ jobs:
           if ($LASTEXITCODE -ne 0) { throw "$t failed under ASAN (exit $LASTEXITCODE)" }
         }
 
+  # Build and run the autotools regression tests under MSYS2 MinGW64. MinGW
+  # defines _WIN32, so wolfssh/settings.h turns on USE_WINDOWS_API and the
+  # Windows-only coverage in tests/regress.c (TestSftpWindowsOpenFlagMatrix,
+  # which walks the RecvOpen CREAT/EXCL/TRUNC/APPEND matrix against the
+  # CreateFile() disposition table) actually compiles and runs. The MSVC
+  # solution has no regress project and regress.c does not build with cl (it
+  # uses arpa/inet.h and unistd.h), so without this job that matrix runs in no
+  # CI at all. wolfsshd is left out of the build: its autotools path is not
+  # MinGW-clean and the MSVC solution already covers it.
+  mingw-regress:
+    name: MSYS2 MinGW64 regression tests
+    runs-on: windows-latest
+    timeout-minutes: 40
+
+    defaults:
+      run:
+        shell: msys2 {0}
+
+    steps:
+    - name: Set up MSYS2 MinGW64
+      uses: msys2/setup-msys2@v2
+      with:
+        msystem: MINGW64
+        update: false
+        install: >-
+          base-devel
+          autotools
+          git
+          mingw-w64-x86_64-gcc
+          mingw-w64-x86_64-pkgconf
+
+    - name: Checkout wolfssl
+      uses: actions/checkout@v4
+      with:
+        repository: wolfssl/wolfssl
+        path: wolfssl
+
+    - name: Build and install wolfssl
+      working-directory: wolfssl
+      run: |
+        ./autogen.sh
+        # --enable-all pulls in --enable-crl-monitor, which wolfSSL's configure
+        # rejects on MinGW (it is limited to linux, OS X, and freebsd). Turn it
+        # back off explicitly; wolfSSH does not use the CRL monitor.
+        ./configure --enable-all --disable-crl-monitor \
+          --enable-static --disable-shared \
+          --prefix="$HOME/wolfssl-install"
+        make -j$(nproc)
+        make install
+
+    - name: Checkout wolfssh
+      uses: actions/checkout@v4
+      with:
+        path: wolfssh
+
+    - name: Build and run the regression tests
+      working-directory: wolfssh
+      run: |
+        # Run autoreconf directly instead of ./autogen.sh: for a git checkout
+        # autogen.sh exports WARNINGS="all,error", turning autotools warnings
+        # into errors that the MSYS2 automake can trip on.
+        autoreconf -ivf
+        ./configure --enable-sftp \
+          CPPFLAGS="-I$HOME/wolfssl-install/include" \
+          LDFLAGS="-L$HOME/wolfssl-install/lib"
+        make -j$(nproc) tests/regress.test tests/unit.test
+        ./tests/regress.test
+        ./tests/unit.test