CI: Add macOS builds

This is a sync from testing repo.

.github/workflows/build.yml

@@ -16,7 +16,7 @@ on:
   pull_request:
 
 jobs:
-  build:
+  build-linux:
     runs-on: ubuntu-18.04
     env:
       DOCKER_BUILDKIT: 1
@@ -65,3 +65,50 @@ jobs:
         run: |
           cd testing
           ./cibuild.sh -x -G testlist/${{matrix.boards}}.dat
+
+  build-macos:
+    runs-on: macos-10.15
+
+    strategy:
+      matrix:
+        boards: [arm-13, mips-riscv-x86-xtensa, sim]
+
+    steps:
+    - name: Checkout nuttx repo
+      uses: actions/checkout@v2
+      with:
+        repository: apache/incubator-nuttx
+        path: nuttx
+        fetch-depth: 0
+
+    - name: Fetch nuttx tags
+      run: |
+        cd nuttx
+        git fetch --tags
+
+    - name: Checkout apps repo
+      uses: actions/checkout@v2
+      with:
+        repository: apache/incubator-nuttx-apps
+        path: apps
+        fetch-depth: 0
+
+    - name: Checkout testing repo
+      uses: actions/checkout@v2
+      with:
+        repository: apache/incubator-nuttx-testing
+        path: testing
+
+    - name: Restore cache
+      id: cache-tools
+      uses: actions/cache@v1
+      env:
+        cache-name: ${{ runner.os }}-cache-tools
+      with:
+        path: prebuilt
+        key: ${{ runner.os }}-tools-${{ hashFiles('./testing/cibuild.sh') }}
+
+    - name: Run builds
+      run: |
+        cd testing
+        ./cibuild.sh -i -x -G testlist/${{matrix.boards}}.dat