github/workflows: add freebsd CI

.github/workflows/build.yml

@@ -94,3 +94,46 @@ jobs:
         if: ${{ failure() }}
         run: |
           cat ./build/config.log
+
+  freebsd:
+    runs-on: macos-10.15 # until https://github.com/actions/runner/issues/385
+    steps:
+    - uses: actions/checkout@v2
+    - name: Test in FreeBSD VM
+      uses: vmactions/freebsd-vm@v0.1.5 # aka FreeBSD 13.0
+      with:
+        usesh: true
+        prepare: |
+            # Requested in ci/build-freebsd.sh
+            pkg install -y \
+                evdev-proto \
+                ffmpeg \
+                libplacebo \
+                libxkbcommon \
+                luajit \
+                openal-soft \
+                pkgconf \
+                python3 \
+                sdl2 \
+                vulkan-headers \
+                wayland-protocols \
+                #
+            # Optionally auto-enabled
+            pkg install -y \
+                alsa-lib \
+                jackit \
+                libXv \
+                libarchive \
+                libbluray \
+                libcaca \
+                libcdio-paranoia \
+                libdvdnav \
+                mujs \
+                pulseaudio \
+                rubberband \
+                sekrit-twc-zimg \
+                uchardet \
+                v4l_compat \
+                #
+        run: |
+          ./ci/build-freebsd.sh