Try building on cygwin

.github/workflows/cygwin.yml

@@ -0,0 +1,43 @@
+
+name: Test on Cygwin 
+on: [push, pull_request]
+
+jobs:
+  cygwin_build_test:
+    runs-on: windows-latest
+    steps:
+        - name: Install Cygwin
+          uses: cygwin/cygwin-install-action
+          with:
+            platform: x86_64
+            install-dir: 'C:\tools\cygwin'
+            packages: >-
+                python39-devel python39-pip python-pip-wheel python-setuptools-wheel
+                gcc-fortran git dash
+
+        - name: Set Windows PATH
+          uses: egor-tensin/cleanup-path
+          with:
+            dirs: 'C:\tools\cygwin\bin;C:\tools\cygwin\lib\lapack'
+        - name: Verify that bash is Cygwin bash
+          run: |
+            command bash
+            bash -c "uname -svrmo"
+        - name: Tell Cygwin's git about this repository.
+          run: |
+            dash -c "which git; /usr/bin/git config --system --add safe.directory /cygdrive/d/a/gfort2py/gfort2py"
+        - name: Verify python version
+          # Make sure it's the Cygwin one, not a Windows one
+          run: |
+            dash -c "which python3.9; /usr/bin/python3.9 --version -V"    
+        - name: Install dependencies
+          run: |
+            dash -c "/usr/bin/python3.9 -m pip install --upgrade pip"
+            dash -c "/usr/bin/python3.9 -m pip install build wheel pytest"
+        - name: Install 
+          run: |
+            dash -c "/usr/bin/python3.9 -m pip install ."
+        - name: Run tests
+          run: |
+              dash -c "/usr/bin/python3.9 -m pytest -v"
+