Preliminary github actions support

.github/workflows/build.yml

@@ -0,0 +1,43 @@
+name: Build
+on: [push]
+jobs:
+  build-mac:
+    runs-on: macos-latest
+    steps:
+      - run: echo "This job is now running on a ${{ runner.os }} server hosted by GitHub!"
+      - run: echo "The name of your branch is ${{ github.ref }} and your repository is ${{ github.repository }}."
+      - name: Check out repository code
+        uses: actions/checkout@v2
+      - run: brew install automake
+      - run: autoreconf -i
+      - run: ./configure --enable-warning-as-error
+      - run: make all
+      - run: make dist
+  build-linux:
+    runs-on: ubuntu-latest
+    steps:
+      - run: echo "This job is now running on a ${{ runner.os }} server hosted by GitHub!"
+      - run: echo "The name of your branch is ${{ github.ref }} and your repository is ${{ github.repository }}."
+      - name: Check out repository code
+        uses: actions/checkout@v2
+      - run: autoreconf -i
+      - run: ./configure --enable-warning-as-error
+      - run: make all
+      - run: make dist
+  build-win:
+    runs-on: windows-latest
+    defaults:
+      run:
+        shell: msys2 {0}
+    steps:
+      - uses: actions/checkout@v2
+      - uses: msys2/setup-msys2@v2
+        with:
+          msystem: MINGW64
+          update: true
+          install: mingw-w64-x86_64-gcc autoconf automake make
+      - run: autoreconf -i
+      - run: ./configure --enable-warning-as-error
+      - run: make all
+      - run: make dist
+