[ci] Add macOS GitHub workflow

To collect codecov coverage on macOS as well (hopefully it will run the
macOS-specific tests).

.github/workflows/macos-ci.yml

@@ -0,0 +1,27 @@
+name: macos-ci
+
+on:
+  push:
+    branches: [ main ]
+  pull_request:
+    branches: [ main ]
+
+jobs:
+  build:
+    runs-on: macos-10.15
+
+    steps:
+    - uses: actions/checkout@v2
+    - name: install dependencies
+      run: HOMEBREW_NO_AUTO_UPDATE=1 brew install pkg-config freetype glib cairo icu4c graphite2 gobject-introspection gtk-doc ninja gcovr
+    - run: pip3 install meson fonttools --upgrade
+    - name: run
+      run: PKG_CONFIG_PATH="/usr/local/opt/icu4c/lib/pkgconfig:/usr/local/opt/libffi/lib/pkgconfig" meson build -Db_coverage=true -Dcoretext=enabled -Dgraphite=enabled -Dauto_features=enabled -Dchafa=disabled -Doptimization=2
+    - name: ci
+      run: meson test --print-errorlogs -Cbuild
+
+    - name: cov
+      run: ninja -Cbuild coverage
+    - uses: codecov/codecov-action@v1
+      with:
+        file: build/meson-logs/coverage.xml