test macos build

.github/workflows/macos.yml

@@ -0,0 +1,19 @@
+name: macOS Build
+on: [push, pull_request]
+
+jobs:
+  build:
+    runs-on: macOS-latest
+    steps:
+      - uses: actions/checkout@v2
+        with:
+          fetch-depth: 0
+
+      - name: Install dependencies
+        run: |
+          brew install meson ninja
+
+      - name: Build Aegisub
+        run: |
+          MSYSTEM= meson builddir -Ddefault_library=static
+          ninja -C builddir