Add macOS build action

.github/workflows/macos.yml

@@ -0,0 +1,26 @@
+name: macOS
+
+on: [push, pull_request]
+
+jobs:
+  build:
+
+    runs-on: macos-latest
+
+    steps:
+    - uses: actions/checkout@v2
+    - name: dependencies
+      run: brew update && brew install flac opus libvorbis libsoxr
+    - name: cache boost
+      id: cache-boost
+      uses: actions/cache@v2
+      with:
+        path: boost_1_73_0
+        key: ${{ runner.os }}-boost
+    - name: get boost
+      if: steps.cache-boost.outputs.cache-hit != 'true'
+      run: wget https://dl.bintray.com/boostorg/release/1.73.0/source/boost_1_73_0.tar.bz2 && tar xjf boost_1_73_0.tar.bz2
+    - name: cmake build
+      run: cmake -S . -B build -DBOOST_ROOT=boost_1_73_0
+    - name: cmake make
+      run: cmake --build build