add job for building win32 version

.github/workflows/mingw.yml

@@ -0,0 +1,29 @@
+# This is a basic workflow to help you get started with Actions
+
+name: CI
+
+# Controls when the action will run. Triggers the workflow on push or pull request
+# events but only for the master branch
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+
+# A workflow run is made up of one or more jobs that can run sequentially or in parallel
+jobs:
+  # This workflow contains a single job called "build"
+  build:
+    # The type of runner that the job will run on
+    runs-on: ubuntu-latest
+
+    # Steps represent a sequence of tasks that will be executed as part of the job
+    steps:
+      # Checks-out your repository under $GITHUB_WORKSPACE, so your job can access it
+      - uses: actions/checkout@v2
+
+      - name: install packages
+        run: sudo apt-get install gcc-mingw-w64-i686 mingw-w64-tools
+
+      - name: build miniupnpc for win32
+        run: make -C miniupnpc -f Makefile.mingw DLLWRAP=i686-w64-mingw32-dllwrap CC=i686-w64-mingw32-gcc AR=i686-w64-mingw32-ar"