Add CI workflow for multiple OS environments

.github/workflows/ci.yml

@@ -0,0 +1,49 @@
+name: ci
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+
+permissions:
+  contents: read
+
+jobs:
+  unix:
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-24.04, ubuntu-24.04-arm, macos-15, macos-15-intel]
+    runs-on: ${{ matrix.os }}
+    steps:
+      - uses: actions/checkout@v6
+      - run: ./configure && make
+      - run: ./mikusays -V && ./mikusays "hi"
+
+  windows:
+    runs-on: windows-2025
+    defaults:
+      run:
+        shell: msys2 {0}
+    steps:
+      - uses: actions/checkout@v6
+      - uses: msys2/setup-msys2@v2
+        with:
+          msystem: UCRT64
+          install: mingw-w64-ucrt-x86_64-gcc make
+      - run: ./configure && make
+      - run: ./mikusays.exe -V && ./mikusays.exe "hi"
+
+  # runs in a real FreeBSD VM with its stock cc + BSD make
+  freebsd:
+    runs-on: ubuntu-24.04
+    steps:
+      - uses: actions/checkout@v6
+      - uses: vmactions/freebsd-vm@v1
+        with:
+          usesh: true
+          run: |
+            ./configure
+            make
+            ./mikusays -V
+            ./mikusays "hi"